Al2O3-rare earth oxide-ZrO2/HfO2 materials, and methods of making and using the same

ABSTRACT

Al 2 O 3 -rare earth oxide-ZrO 2 /HfO 2  ceramics (including glasses, crystalline ceramics, and glass-ceramics) and methods of making the same. Ceramics according to the present invention can be made, formed as, or converted into glass beads, articles (e.g., plates), fibers, particles, and thin coatings. The particles and fibers are useful, for example, as thermal insulation, filler, or reinforcing material in composites (e.g., ceramic, metal, or polymeric matrix composites). The thin coatings can be useful, for example, as protective coatings in applications involving wear, as well as for thermal management. Certain ceramic particles according to the present invention can be are particularly useful as abrasive particles.

[0001] This application is a continuation-in-part of U.S. Ser. No.09/922,527, filed Aug. 2, 2001, the disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to Al₂O₃-rare earth oxide-ZrO₂/HfO₂(including amorphous materials (including glasses), crystallineceramics, and glass-ceramics) and methods of making the same.

DESCRIPTION OF RELATED ART

[0003] A large number of amorphous (including glass) and glass-ceramiccompositions are known. The majority of oxide glass systems utilizewell-known glass-formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃,and V₂O₅ to aid in the formation of the glass. Some of the glasscompositions formed with these glass-formers can be heat-treated to formglass-ceramics. The upper use temperature of glasses and glass-ceramicsformed from such glass formers is generally less than 1200° C.,typically about 700-800° C. The glass-ceramics tend to be moretemperature resistant than the glass from which they are formed.

[0004] In addition, many properties of known glasses and glass-ceramicsare limited by the intrinsic properties of glass-formers. For example,for SiO₂, B₂O₃, and P₂O₅-based glasses and glass-ceramics, the Young'smodulus, hardness, and strength are limited by such glass-formers. Suchglass and glass-ceramics generally have inferior mechanical propertiesas compared, for example, to Al₂O₃ or ZrO₂. Glass-ceramics having anymechanical properties similar to that of Al₂O₃ or ZrO₂ would bedesirable.

[0005] Although some non-conventional glasses such as glasses based onrare earth oxide-aluminum oxide (see, e.g., PCT application havingpublication No. WO 01/27046 A1, published Apr. 19, 2001, and JapaneseDocument No. JP 2000-045129, published Feb. 15, 2000) are known,additional novel glasses and glass-ceramic, as well as use for bothknown and novel glasses and glass-ceramics is desired.

[0006] In another aspect, a variety of abrasive particles (e.g., diamondparticles, cubic boron nitride particles, fused abrasive particles, andsintered, ceramic abrasive particles (including sol-gel-derived abrasiveparticles) known in the art. In some abrading applications, the abrasiveparticles are used in loose form, while in others the particles areincorporated into abrasive products (e.g., coated abrasive products,bonded abrasive products, non-woven abrasive products, and abrasivebrushes). Criteria used in selecting abrasive particles used for aparticular abrading application include: abrading life, rate of cut,substrate surface finish, grinding efficiency, and product cost.

[0007] From about 1900 to about the mid-1980's, the premier abrasiveparticles for abrading applications such as those utilizing coated andbonded abrasive products were typically fused abrasive particles. Thereare two general types of fused abrasive particles: (1) fused alphaalumina abrasive particles (see, e.g., U.S. Pat. Nos. 1,161,620(Coulter), 1,192,709 (Tone), 1,247,337 (Saunders et al.), 1,268,533(Allen), and 2,424,645 (Baumann et al.)) and (2) fused (sometimes alsoreferred to as “co-fused”) alumina-zirconia abrasive particles (see,e.g., U.S. Pat. Nos. 3,891,408 (Rowse et al.), 3,781,172 (Pett et al.),3,893,826 (Quinan et al.), 4,126,429 (Watson), 4,457,767 (Poon et al.),and 5,143,522 (Gibson et al.))(also see, e.g., U.S. Pat. Nos. 5,023,212(Dubots et. al) and 5,336,280 (Dubots et. al) which report the certainfused oxynitride abrasive particles). Fused alumina abrasive particlesare typically made by charging a furnace with an alumina source such asaluminum ore or bauxite, as well as other desired additives, heating thematerial above its melting point, cooling the melt to provide asolidified mass, crushing the solidified mass into particles, and thenscreening and grading the particles to provide the desired abrasiveparticle size distribution. Fused alumina-zirconia abrasive particlesare typically made in a similar manner, except the furnace is chargedwith both an alumina source and a zirconia source, and the melt is morerapidly cooled than the melt used to make fused alumina abrasiveparticles. For fused alumina-zirconia abrasive particles, the amount ofalumina source is typically about 50-80 percent by weight, and theamount of zirconia, 50-20 percent by weight zirconia. The processes formaking the fused alumina and fused alumina abrasive particles mayinclude removal of impurities from the melt prior to the cooling step.

[0008] Although fused alpha alumina abrasive particles and fusedalumina-zirconia abrasive particles are still widely used in abradingapplications (including those utilizing coated and bonded abrasiveproducts, the premier abrasive particles for many abrading applicationssince about the mid-1980's are sol-gel-derived alpha alumina particles(see, e.g., U.S. Pat. Nos. 4,314,827 (Leitheiser et al.), 4,518,397(Leitheiser et al.), 4,623,364 (Cottringer et al.), 4,744,802(Schwabel), 4,770,671 (Monroe et al.), 4,881,951 (Wood et al.),4,960,441 (Pellow et al.), 5,139,978 (Wood), 5,201,916 (Berg et al.),5,366,523 (Rowenhorst et al.), 5,429,647 (Larmie), 5,547,479 (Conwell etal.), 5,498,269 (Larmie), 5,551,963 (Larmie), and 5,725,162 (Garg etal.)).

[0009] The sol-gel-derived alpha alumina abrasive particles may have amicrostructure made up of very fine alpha alumina crystallites, with orwithout the presence of secondary phases added. The grinding performanceof the sol-gel derived abrasive particles on metal, as measured, forexample, by life of abrasive products made with the abrasive particleswas dramatically longer than such products made from conventional fusedalumina abrasive particles.

[0010] Typically, the processes for making sol-gel-derived abrasiveparticles are more complicated and expensive than the processes formaking conventional fused abrasive particles. In general,sol-gel-derived abrasive particles are typically made by preparing adispersion or sol comprising water, alumina monohydrate (boehmite), andoptionally peptizing agent (e.g., an acid such as nitric acid), gellingthe dispersion, drying the gelled dispersion, crushing the drieddispersion into particles, screening the particles to provide thedesired sized particles, calcining the particles to remove volatiles,sintering the calcined particles at a temperature below the meltingpoint of alumina, and screening and grading the particles to provide thedesired abrasive particle size distribution. Frequently a metal oxidemodifier(s) is incorporated into the sintered abrasive particles toalter or otherwise modify the physical properties and/or microstructureof the sintered abrasive particles.

[0011] There are a variety of abrasive products (also referred to“abrasive articles”) known in the art. Typically, abrasive productsinclude binder and abrasive particles secured within the abrasiveproduct by the binder. Examples of abrasive products include: coatedabrasive products, bonded abrasive products, nonwoven abrasive products,and abrasive brushes.

[0012] Examples of bonded abrasive products include: grinding wheels,cutoff wheels, and honing stones. The main types of bonding systems usedto make bonded abrasive products are: resinoid, vitrified, and metal.Resinoid bonded abrasives utilize an organic binder system (e.g.,phenolic binder systems) to bond the abrasive particles together to formthe shaped mass (see, e.g., U.S. Pat. Nos. 4,741,743 (Narayanan et al.),4,800,685 (Haynes et al.), 5,037,453 (Narayanan et al.), and 5,110,332(Narayanan et al.)). Another major type are vitrified wheels in which aglass binder system is used to bond the abrasive particles together mass(see, e.g., U.S. Pat. Nos. 4,543,107 (Rue), 4,898,587 (Hay et al.),4,997,461 (Markhoff-Matheny et al.), and 5,863,308 (Qi et al.)). Theseglass bonds are usually matured at temperatures between 900° C. to 1300°C. Today vitrified wheels utilize both fused alumina and sol-gel-derivedabrasive particles. However, fused alumina-zirconia is generally notincorporated into vitrified wheels due in part to the thermal stabilityof alumina-zirconia. At the elevated temperatures at which the glassbonds are matured, the physical properties of alumina-zirconia degrade,leading to a significant decrease in their abrading performance. Metalbonded abrasive products typically utilize sintered or plated metal tobond the abrasive particles.

[0013] The abrasive industry continues to desire abrasive particles andabrasive products that are easier to make, cheaper to make, and/orprovide performance advantage(s) over conventional abrasive particlesand products.

SUMMARY OF THE INVENTION

[0014] The present invention provides ceramics comprising (on atheoretical oxide basis; e.g., may be present as a reaction product(e.g., CeAl₁₁O₁₈)), Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,including glass, crystalline ceramic (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO) and/or ZrO₂), and glass-ceramicmaterials, wherein in amorphous materials not having a T_(g), certainpreferred embodiments have x, y, and z dimensions each perpendicular toeach other, and wherein each of the x, y, and z dimensions is at least 5mm (in some embodiments at least 10 mm), the x, y, and z dimensions isat least 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers,50 micrometers, 75 micrometers, 100 micrometers, 150 micrometers, 200micrometers, 250 micrometers, 500 micrometers, 1000 micrometers, 2000micrometers, 2500 micrometers, 1 mm, 5 mm, or even at least 10 mm. Thex, y, and z dimensions of a material are determined either visually orusing microscopy, depending on the magnitude of the dimensions. Thereported z dimension is, for example, the diameter of a sphere, thethickness of a coating, or the longest length of a prismatic shape.

[0015] Some embodiments of ceramic materials according to the presentinvention may comprise, for example, less than 40 (35, 30, 25, 20, 15,10, 5, 3, 2, 1, or even zero) percent by weight traditional glassformers such as SiO₂, As₂O₃, B₂O₃, P₂O₅, GeO₂, TeO₂, V₂ O₅, and/orcombinations thereof, based on the total weight of the ceramic. Ceramicsaccording to the present invention may comprise, for example, at least1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80,85, 90, 95, or even 100 percent by volume amorphous material. Someembodiments of ceramics according to the present invention may comprise,for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume crystalline ceramic, based on the total volume of the ceramic.

[0016] Typically, ceramics according to the present invention comprisesat least 30 percent by weight of the Al₂O₃, based on the total weight ofthe ceramic. More typically, ceramics according to the present inventioncomprise at least 30 (desirably, in a range of about 30 to about 60)percent by weight Al₂O₃, at least 20 (about 20 to about 65) percent byweight REO, and at least 5 (about 5 to about 30) percent by weight ZrO₂and/or HfO₂, based on the total weight of the ceramic. The weight ratioof ZrO₂:HfO₂ can range of 1:zero (i.e., all ZrO₂; no HfO₂) to zero:1, aswell as, for example, at least about 99, 98, 97, 96, 95, 90, 85, 80, 75,70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 20, 15, 10, and 5 parts (byweight) ZrO₂ and a corresponding amount of HfO₂ (e.g., at least about 99parts (by weight) ZrO₂ and not greater than about 1 part HfO₂) and atleast about 99, 98, 97, 96, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45,40, 35, 30, 25, 20, 20, 15, 10, and 5 parts HfO₂ and a correspondingamount of ZrO₂. Optionally, ceramics according to the present inventionfurther comprise Y₂O₃.

[0017] For ceramics according to the present invention comprisingcrystalline ceramic, some embodiments include those wherein the ceramic(a) exhibits a microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃.REO)and/or ZrO₂) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, even less than 300,200, or 150 nanometers; and in some embodiments, less than 100, 75, 50,25, or 20 nanometers), and (b) is free of at least one of eutecticmicrostructure features (i.e., is free of colonies and lamellarstructure) or a non-cellular microstructure. It is also within the scopeof the present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0018] Some embodiments of the present invention include amorphousmaterial comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the amorphous material collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, based on the total weight of theamorphous material.

[0019] Some embodiments of the present invention include amorphousmaterial comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the amorphous material collectively comprisesthe Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight SiO₂ andless than 20 (preferably, less than 15, 10, 5, or even 0) percent byweight B₂O₃, based on the total weight of the amorphous material.

[0020] Some embodiments of the present invention include amorphousmaterial comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the amorphous material collectively comprisesthe Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and less than 40(preferably, less than 35, 30, 25, 20, 15, 10, 5, or even 0) percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe amorphous material.

[0021] Some embodiments of the present invention include ceramiccomprising amorphous material (e.g., at least 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume amorphous material), the amorphous material comprisingAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 80 (85,90, 95, 97, 98, 99, or even 100) percent by weight of the amorphousmaterial collectively comprises the Al₂O₃, REO, and at least one of ZrO₂or HfO₂, based on the total weight of the amorphous material.

[0022] Some embodiments of the present invention include ceramiccomprising amorphous material (e.g., at least 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume glass), the amorphous material comprising Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75, 80,85, 90, 95, 97, 98, 99, or even 100) percent by weight of the amorphousmaterial collectively comprises the Al₂O₃, REO, and at least one of ZrO₂or HfO₂, and less than 20 preferably, less than 15, 10, 5, or even 0)percent by weight SiO₂, and less than 20 (preferably, less than 15, 10,5, or even 0) percent by weight B₂O₃, based on the total weight of theamorphous material. The ceramic may further comprise crystalline ceramic(e.g., at least 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30,25, 20, 15, 10, 5, 3, 2, or 1 percent by volume crystalline ceramic).

[0023] Some embodiments of the present invention include ceramiccomprising amorphous material (e.g., at least 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume glass), the amorphous material comprising Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75, 80,85, 90, 95, 97, 98, 99, or even 100) percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,and less than 40 (preferably, less than 35, 30, 25, 20, 15, 10, 5, oreven 0) percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the amorphous material. The ceramic may furthercomprise crystalline ceramic (e.g., at least 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume crystalline ceramic).

[0024] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theglass-ceramic collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass-ceramic. Theglass-ceramic may comprise, for example, at least 1, 2, 3, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95percent by volume glass. The glass-ceramic may comprise, for example, atleast 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35,30, 25, 20, 15, 10, or 5 percent by volume crystalline ceramic.

[0025] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass-ceramic collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 20 (preferably, lessthan 15, 10, 5, or even 0) percent by weight SiO₂ and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight B₂O₃,based on the total weight of the glass-ceramic. The glass-ceramic maycomprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass.The glass-ceramic may comprise, for example, at least 99, 98, 97, 95,90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

[0026] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass-ceramic collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 40 (preferably, lessthan 35, 30, 25, 20, 15, 10, 5, or even 0) percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass-ceramic. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, percent by volume amorphous material. The glass-ceramic maycomprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volumecrystalline ceramic.

[0027] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃REO) and/or ZrO₂) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than 300,200, or 150 nanometers; and in some embodiments, less than 100, 75, 50,25, or 20 nanometers), and (b) is free of eutectic microstructurefeatures. Some embodiments of the present invention includeglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein the glass-ceramic (a) exhibits a non-cellular microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃ REO) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers). The glass-ceramic maycomprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, percent by volume amorphousmaterial. The glass-ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, or 5 percent by volume crystalline ceramic. It is also within thescope of the present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0028] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the crystallineceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, whereinat least 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight ofthe crystalline ceramic collectively comprises the Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, based on the total weight of the crystallineceramic. Some desirable embodiments include those wherein the ceramic(a) exhibits a microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃ REO)and/or ZrO₂) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than 300,200, or 150 nanometers; and in some embodiments, less than 100, 75, 50,25, or 20 nanometers), and (b) is free of eutectic microstructurefeatures. In another aspect, some desirable embodiments include thosewherein the ceramic (a) exhibits a non-cellular microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃ REO) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers). The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeglass. It is also within the scope of the present invention for someembodiments to have at least one crystalline phase within a specifiedaverage crystallite value and at least one (different) crystalline phaseoutside of a specified average crystallite value.

[0029] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the crystallineceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, whereinat least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100)percent by weight of the crystalline ceramic collectively comprises theAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight SiO₂ andless than 20 (preferably, less than 15, 10, 5, or even 0) percent byweight B₂O₃, based on the total weight of the crystalline ceramic. Somedesirable embodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, or even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume amorphous material. It is also within the scope ofthe present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0030] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the crystallineceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, whereinat least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100)percent by weight of the crystalline ceramic collectively comprises theAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, and less than 40(preferably, less than 35, 30, 25, 20, 15, 10, 5, or even 0) percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe crystalline ceramic. Some desirable embodiments include thosewherein the ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃ REO) and/or ZrO₂) having an average crystallite size ofless than 1 micrometer (typically, less than 500 nanometers, or evenless than less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume amorphous material. It is also within the scope ofthe present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0031] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂. some desirableembodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, or even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume amorphous material. It is also within the scope ofthe present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0032] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises the Al₂O₃, REO, and at least one of ZrO₂or HfO₂, based on the total weight of the ceramic. Some desirableembodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, or even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃.REO) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume amorphous material. It is also within the scope ofthe present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0033] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the ceramic collectively comprises the Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, and less than 20 (preferably, less than 15,10, 5, or even 0) percent by weight SiO₂ and less than 20 (preferably,less than 15, 10, 5, or even 0) percent by weight B₂O₃, based on thetotal weight of the ceramic. Some desirable embodiments include thosewherein the ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃ REO) and/or ZrO₂) having an average crystallite size ofless than 1 micrometer (typically, less than 500 nanometers, or evenless than 300, 200, or 150 nanometers; and in some embodiments, lessthan 100, 75, 50, 25, or 20 nanometers), and (b) is free of eutecticmicrostructure features. Some embodiments of the present inventioninclude those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers). The ceramicmay comprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70,65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume glass. It is also within the scope of the present invention forsome embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

[0034] Some embodiments of the present invention include ceramiccomprising crystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic), the ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the ceramic collectively comprises the Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, and less than 40 (preferably, less than 35,30, 25, 20, 15, 10, 5, or even 0) percent by weight collectively SiO₂,B₂O₃, and P₂O₅, based on the total weight of the ceramic. Some desirableembodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, or even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume amorphous material. It is also within the scope ofthe present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0035] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO_(2,) wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃REO) and/or ZrO₂) having an average crystallite size of less than 200nanometers (150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) and (b) has a density of at least 90% (95%, 96%, 97%, 98%,99%, 99.5%, or 100%) of theoretical density. Some embodiments can befree of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

[0036] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃REO) and/or ZrO₂), wherein none of the crystallites are greater than 200nanometers (150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite size value and at least one (different)crystalline phase outside of a specified crystallite size value.

[0037] Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃REO) and/or ZrO₂), wherein at least a portion of the crystallites arenot greater than 150 nanometers (100 nanometers, 75 nanometers, or even50 nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%,99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite value and at least one (different)crystalline phase outside of a specified crystallite value.

[0038] Some embodiments of the present invention include fullycrystallized glass-ceramic comprising Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, wherein the glass-ceramic (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃ REO) and/or ZrO₂) having an average crystallitesize not greater than 1 micrometer (500 nanometers, 300 nanometers, 200nanometers, 150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite value and at least one (different)crystalline phase outside of a specified crystallite value.

[0039] For ceramics according to the present invention comprisingcrystalline ceramic, some embodiments include those comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites (e.g., crystallites of acomplex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂) having anaverage crystallite size of less than 200 nanometers (150 nanometers,100 nanometers, 75 nanometers, or even 50 nanometers) and (b) has adensity of at least 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) oftheoretical density. Some embodiments can be free of at least one ofeutectic microstructure features or a non-cellular microstructure. It isalso within the scope of the present invention for some embodiments tohave at least one crystalline phase within a specified averagecrystallite value and at least one (different) crystalline phase outsideof a specified average crystallite value.

[0040] For ceramics according to the present invention comprisingcrystalline ceramic, some embodiments include those comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites (e.g., crystallites of acomplex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂), whereinnone of the crystallites are greater than 200 nanometers (150nanometers, 100 nanometers, 75 nanometers, or even 50 nanometers) insize and (b) has a density of at least 90% (95%, 96%, 97%, 98%, 99%,99.5%, or 100%) of theoretical density. Some embodiments can be free ofat least one of eutectic microstructure features or a non-cellularmicrostructure. It is also within the scope of the present invention forsome embodiments to have at least one crystalline phase within aspecified crystallite value and at least one (different) crystallinephase outside of a specified crystallite value.

[0041] For ceramics according to the present invention comprisingcrystalline ceramic, some embodiments include those comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites (e.g., crystallites of acomplex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂), whereinat least a portion of the crystallites are not greater than 150nanometers (100 nanometers, 75 nanometers, or even 50 nanometers) insize and (b) has a density of at least 90% (95%, 96%, 97%, 98%, 99%,99.5%, or 100%) of theoretical density. Some embodiments can be free ofat least one of eutectic microstructure features or a non-cellularmicrostructure. It is also within the scope of the present invention forsome embodiments to have at least one crystalline phase within aspecified crystallite value and at least one (different) crystallinephase outside of a specified crystallite value.

[0042] For ceramics according to the present invention comprisingcrystalline ceramic, some embodiments include those comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites (e.g., crystallites of acomplex metal oxide(s) (e.g., complex Al₂O₃ REO) and/or ZrO₂) having anaverage crystallite size not greater than 1 micrometer (500 nanometers,300 nanometers, 200 nanometers, 150 nanometers, 100 nanometers, 75nanometers, or even 50 nanometers) in size and (b) has a density of atleast 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) of theoreticaldensity. Some embodiments can be free of at least one of eutecticmicrostructure features or a non-cellular microstructure. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified crystallite value andat least one (different) crystalline phase outside of a specifiedcrystallite value.

[0043] Some embodiments of the present invention include a glass-ceramiccomprising alpha Al₂O₃, crystalline ZrO₂, and a first complex Al₂O₃.REO,wherein at least one of the alpha Al₂O₃, the crystalline ZrO₂, or thefirst complex Al₂O₃.REO has an average crystal size not greater than 150nanometers, and wherein the abrasive particles have a density of atleast 90 (in some embodiments at least 95, 96, 97, 98, 99, 99.5, or even100) percent of theoretical density. In some embodiments, preferably atleast 75 (80, 85, 90, 95, 97, or even at least 99) percent of thecrystal sizes by number are not greater than 200 nanometers. In someembodiments preferably, the glass-ceramic further comprises a second,different complex Al₂O₃.REO. In some embodiments preferably, theglass-ceramic further comprises a complex Al₂O₃.Y₂O₃.

[0044] Some embodiments of the present invention include a glass-ceramiccomprising a first complex Al₂O₃.REO, a second, different complexAl₂O₃.REO, and crystalline ZrO₂, wherein for at least one of the firstcomplex Al₂O₃.REO, the second complex Al₂O₃.REO, or the crystallineZrO₂, at least 90 (in some embodiments preferably, 95, or even 100)percent by number of the crystal sizes thereof are not greater than 200nanometers, and wherein the abrasive particles have a density of atleast 90 (in some embodiments at least 95, 96, 97, 98, 99, 99.5, or even100) percent of theoretical density. In some embodiments preferably, theglass-ceramic further comprises a complex Al₂O₃-Y₂O₃.

[0045] Some embodiments of the present invention a glass-ceramiccomprising a first complex Al₂O₃.REO, a second, different complexAl₂O₃.REO, and crystalline ZrO₂, wherein at least one of the firstcomplex Al₂O₃-REO, the second, different complex Al₂O₃.REO, or thecrystalline ZrO₂ has an average crystal size not greater than 150nanometers, and wherein the abrasive particles have a density of atleast 90 (in some embodiments at least 95, 96, 97, 98, 99, 99.5, or even100) percent of theoretical density. In some embodiments, preferably atleast 75 (80, 85, 90, 95, 97, or even at least 99) percent by number ofthe crystal sizes are not greater than 200 nanometers. In someembodiments preferably, the glass-ceramic further comprises a second,different complex Al₂O₃.REO. In some embodiments preferably, theglass-ceramic further comprises a complex Al₂O₃.Y₂O₃.

[0046] Some embodiments of the present invention include abrasiveparticles comprising a glass-ceramic, the glass-ceramic comprising afirst complex Al₂O₃.REO, a second, different complex Al₂O₃.REO, andcrystalline ZrO₂, wherein for at least one of the first complexAl₂O₃.REO, the second, different complex Al₂O₃.REO, or the crystallineZrO₂, at least 90 (in some embodiments preferably, 95, or even 100)percent by number of the crystal sizes thereof are not greater than 200nanometers, and wherein the abrasive particles have a density of atleast 90 (in some embodiments at least 95, 96, 97, 98, 99, 99.5, or even100) percent of theoretical density. In some embodiments preferably, theglass-ceramic further comprises a complex Al₂O₃.Y₂O₃.

[0047] In another aspect, the present invention provides methods formaking ceramics according to the present invention. For example, thepresent invention provides a method for making ceramic according to thepresent invention comprising amorphous material (e.g., glass, or glassand crystalline ceramic including glass-ceramic), the method comprising:

[0048] melting sources of at least Al₂O₃, REO, and at least one of ZrO₂or HfO₂ to provide a melt; and

[0049] cooling the melt to provide ceramic comprising amorphousmaterial. It is also within the scope of the present invention toheat-treat certain amorphous materials or ceramics comprising amorphousmaterial described herein to a ceramic comprising crystalline ceramic(including glass-ceramic) (i.e., such that at least a portion of theamorphous material is converted to a glass-ceramic).

[0050] In this application:

[0051] “amorphous material” refers to material derived from a meltand/or a vapor phase that lacks any long range crystal structure asdetermined by X-ray diffraction and/or has an exothermic peakcorresponding to the crystallization of the amorphous material asdetermined by a DTA (differential thermal analysis) as determined by thetest described herein entitled “Differential Thermal Analysis”;

[0052] “ceramic” includes amorphous material, glass, crystallineceramic, glass-ceramic, and combinations thereof;

[0053] “complex metal oxide” refers to a metal oxide comprising two ormore different metal elements and oxygen (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂,MgAl₂O₄, and Y₃Al₅O₁₂);

[0054] “complex Al₂O₃.metal oxide” refers to a complex metal oxidecomprising, on a theoretical oxide basis, Al₂O₃ and one or more metalelements other than Al (e.g., CeAl₁₁O₁₈ , Dy₃Al₅O₁₂, MgAl₂O₄, andY₃Al₅O₁₂);

[0055] “complex Al₂O₃.Y₂O₃” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and Y₂O₃ (e.g., Y₃Al₅O₁₂);

[0056] “complex Al₂O₃.REO” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and rare earth oxide (e.g.,CeAl₁₁O₁₈ and Dy₃Al₅O₁₂);

[0057] “glass” refers to amorphous material exhibiting a glasstransition temperature;

[0058] “glass-ceramic” refers to ceramic comprising crystals formed byheat-treating amorphous material;

[0059] “T_(g)” refers to the glass transition temperature as determinedby the test described herein entitled “Differential Thermal Analysis”;

[0060] “T_(x)” refers to the crystallization temperature as determinedby the test described herein entitled “Differential Thermal Analysis”;

[0061] “rare earth oxides” refers to cerium oxide (e.g., CeO₂),dysprosium oxide (e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europiumoxide (e.g., Eu₂O₃), gadolinium (e.g., Gd₂O₃), holmium oxide (e.g.,Ho₂O₃), lanthanum oxide (e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃),neodymium oxide (e.g., Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁),samarium oxide (e.g., Sm₂O₃), terbium (e.g., Tb₂O₃), thorium oxide(e.g., Th₄O₇), thulium (e.g., Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃),and combinations thereof;

[0062] “REO” refers to rare earth oxide(s).

[0063] Further, it is understood herein that unless it is stated that ametal oxide (e.g., Al₂O₃, complex Al₂O₃.metal oxide, etc.) iscrystalline, for example, in a glass-ceramic, it may be amorphous,crystalline, or portions amorphous and portions crystalline. For example1f a glass-ceramic comprises Al₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂ may eachbe in an amorphous state, crystalline state, or portions in an amorphousstate and portions in a crystalline state, or even as a reaction productwith another metal oxide(s) (e.g., unless it is stated that, forexample, Al₂O₃ is present as crystalline Al₂O₃ or a specific crystallinephase of Al₂O₃ (e.g., alpha Al₂O₃), it may be present as crystallineAl₂O₃ and/or as part of one or more crystalline complex Al₂O₃.metaloxides.

[0064] Further, it is understood that glass-ceramics formed by heatingamorphous material not exhibiting a T_(g) may not actually compriseglass, but rather may comprise the crystals and amorphous material thatdoes not exhibiting a T_(g).

[0065] Ceramics articles according to the present invention can be made,formed as, or converted into glass beads (e.g., beads having diametersof at least 1 micrometers, 5 micrometers, 10 micrometers, 25micrometers, 50 micrometers, 100 micrometers, 150 micrometers, 250micrometers, 500 micrometers, 750 micrometers, 1 mm, 5 mm, or even atleast 10 mm), articles (e.g., plates), fibers, particles, and coatings(e.g., thin coatings). The glass beads can be useful, for example, inreflective devices such as retroreflective sheeting, alphanumericplates, and pavement markings. The particles and fibers are useful, forexample, as thermal insulation, filler, or reinforcing material incomposites (e.g., ceramic, metal, or polymeric matrix composites). Thethin coatings can be useful, for example, as protective coatings inapplications involving wear, as well as for thermal management. Examplesof articles according of the present invention include kitchenware(e.g., plates), dental brackets, and reinforcing fibers, cutting toolinserts, abrasive materials, and structural components of gas engines,(e.g., valves and bearings). Other articles include those having aprotective coating of ceramic on the outer surface of a body or othersubstrate. Certain ceramic particles according to the present inventioncan be particularly useful as abrasive particles. The abrasive particlescan be incorporated into an abrasive article, or used in loose form.

[0066] Abrasive articles according to the present invention comprisebinder and a plurality of abrasive particles, wherein at least a portionof the abrasive particles are the abrasive particles according to thepresent invention. Exemplary abrasive products include coated abrasivearticles, bonded abrasive articles (e.g., wheels), non-woven abrasivearticles, and abrasive brushes. Coated abrasive articles typicallycomprise a backing having first and second, opposed major surfaces, andwherein the binder and the plurality of abrasive particles form anabrasive layer on at least a portion of the first major surface.

[0067] In some embodiments, preferably, at least 5, 10, 15, 20, 25, 30,35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percentby weight of the abrasive particles in an abrasive article are theabrasive particles according to the present invention, based on thetotal weight of the abrasive particles in the abrasive article.

[0068] Abrasive particles are usually graded to a given particle sizedistribution before use. Such distributions typically have a range ofparticle sizes, from coarse particles fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards (i.e., specified nominal grades) include those knownas the American National Standards Institute, Inc. (ANSI) standards,Federation of European Producers of Abrasive Products (FEPA) standards,and Japanese Industrial Standard (JIS) standards. In one aspect, thepresent invention provides a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles are abrasive particles according to the presentinvention. In some embodiments, preferably, at least 5, 10, 15, 20, 25,30, 35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100percent by weight of the plurality of abrasive particles are theabrasive particles according to the present invention, based on thetotal weight of the plurality of abrasive particles.

[0069] The present invention also provides a method of abrading asurface, the method comprising:

[0070] contacting abrasive particles according to the present inventionwith a surface of a workpiece; and

[0071] moving at least one of the abrasive particles according to thepresent invention or the contacted surface to abrade at least a portionof the surface with at least one of the abrasive particles according tothe present invention.

BRIEF DESCRIPTION OF THE DRAWING

[0072]FIG. 1 is an X-Ray diffraction pattern of Example 1 material;

[0073]FIG. 2 is an SEM micrograph of a polished cross-section ofComparative Example A material;

[0074]FIG. 3 is an optical photomicrograph of Example 2 material;

[0075]FIG. 4 is an optical photomicrograph of a section of Example 6hot-pressed material;

[0076]FIG. 5 is an SEM photomicrograph of a polished cross-section ofheat-treated Example 6 material;

[0077]FIG. 6 is an DTA curve of Example 6 material;

[0078]FIG. 7 is an SEM photomicrograph of a polished cross-section ofExample 43 material;

[0079]FIG. 8 is an SEM photomicrograph of a polished cross-section ofExample 47 material;

[0080]FIG. 9 is a fragmentary cross-sectional schematic view of a coatedabrasive article including abrasive particles according to the presentinvention;

[0081]FIG. 10 is a perspective view of a bonded abrasive articleincluding abrasive particles according to the present invention; and

[0082]FIG. 11 is an enlarged schematic view of a nonwoven abrasivearticle including abrasive particles according to the present invention.

DETAILED DESCRIPTION

[0083] In general, ceramics according to the present invention can bemade by heating (including in a flame) the appropriate metal oxidesources to form a melt, desirably a homogenous melt, and then rapidlycooling the melt to provide amorphous materials or ceramic comprisingamorphous materials. Amorphous materials and ceramics comprisingamorphous materials according to the present invention can be made, forexample, by heating (including in a flame) the appropriate metal oxidesources to form a melt, desirably a homogenous melt, and then rapidlycooling the melt to provide amorphous material. Some embodiments ofamorphous materials can be made, for example, by melting the metal oxidesources in any suitable furnace (e.g., an inductive heated furnace, agas-fired furnace, or an electrical furnace), or, for example, in aplasma. The resulting melt is cooled (e.g., discharging the melt into acooling media (e.g., high velocity air jets, liquids, metal plates(including chilled metal plates), metal rolls (including chilled metalrolls), metal balls (including chilled metal balls), and the like)).

[0084] In one method, amorphous materials and ceramic comprisingamorphous materials according to the present invention can be madeutilizing flame fusion as disclosed, for example, in U.S. Pat. No.6,254,981 (Castle), the disclosure of which is incorporated herein byreference. In this method, the metal oxide sources materials are fed(e.g., in the form of particles, sometimes referred to as “feedparticles”) directly into a burner (e.g., a methane-air burner, anacetylene-oxygen burner, a hydrogen-oxygen burner, and like), and thenquenched, for example, in water, cooling oil, air, or the like. Feedparticles can be formed, for example, by grinding, agglomerating (e.g.,spray-drying), melting, or sintering the metal oxide sources. The sizeof feed particles fed into the flame generally determine the size of theresulting amorphous material comprising particles.

[0085] Some embodiments of amorphous materials can also be obtained byother techniques, such as: laser spin melt with free fall cooling,Taylor wire technique, plasmatron technique, hammer and anvil technique,centrifugal quenching, air gun splat cooling, single roller and twinroller quenching, roller-plate quenching and pendant drop meltextraction (see, e.g., Rapid Solidification of Ceramics, Brockway et.al, Metals And Ceramics Information Center, A Department of DefenseInformation Analysis Center, Columbus, Ohio, January, 1984, thedisclosure of which is incorporated here as a reference). Someembodiments of amorphous materials may also be obtained by othertechniques, such as: thermal (including flame or laser orplasma-assisted) pyrolysis of suitable precursors, physical vaporsynthesis (PVS) of metal precursors and mechanochemical processing.

[0086] Useful Al₂O₃.REO-ZrO₂/HfO₂ formulations include those at or neara eutectic composition(s) (e.g., ternary eutectic compositions). Inaddition to Al₂O₃-REO-ZrO₂/HfO₂ compositions disclosed herein, othersuch compositions, including quaternary and other higher order eutecticcompositions, may be apparent to those skilled in the art afterreviewing the present disclosure.

[0087] Sources, including commercial sources, of (on a theoretical oxidebasis) Al₂O₃ include bauxite (including both natural occurring bauxiteand synthetically produced bauxite), calcined bauxite, hydrated aluminas(e.g., boehmite, and gibbsite), aluminum, Bayer process alumina,aluminum ore, gamma alumina, alpha alumina, aluminum salts, aluminumnitrates, and combinations thereof. The Al₂O₃ source may contain, oronly provide, Al₂O₃. Alternatively, the Al₂O₃ source may contain, orprovide Al₂O₃, as well as one or more metal oxides other than Al₂O₃(including materials of or containing complex Al₂O₃.metal oxides (e.g.,Dy₃Al₅O₁₂, Y₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

[0088] Sources, including commercial sources, of rare earth oxidesinclude rare earth oxide powders, rare earth metals, rareearth-containing ores (e.g., bastnasite and monazite), rare earth salts,rare earth nitrates, and rare earth carbonates. The rare earth oxide(s)source may contain, or only provide, rare earth oxide(s). Alternatively,the rare earth oxide(s) source may contain, or provide rare earthoxide(s), as well as one or more metal oxides other than rare earthoxide(s) (including materials of or containing complex rare earthoxide•other metal oxides (e.g., Dy₃Al₅O₁₂, CeAl₅O₁₈, etc.)).

[0089] Sources, including commercial sources, of (on a theoretical oxidebasis) ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

[0090] Optionally, ceramics according to the present invention furthercomprise other oxide metal oxides (i.e., metal oxides other than Al₂O₃,rare earth oxide(s), and ZrO₂/HfO₂). Other useful metal oxide may alsoinclude, on a theoretical oxide basis, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃,GeO₂, Li₂O, MgO, MnO, NiO, Na₂O, Sc₂O₃, SrO, TiO₂, ZnO, and combinationsthereof. Sources, including commercial sources, include the oxidesthemselves, complex oxides, ores, carbonates, acetates, nitrates,chlorides, hydroxides, etc. These metal oxides are added to modify aphysical property of the resulting ceramic and/or improve processing.These metal oxides are typically are added anywhere from 0 to 50% byweight, in some embodiments preferably 0 to 25% by weight and morepreferably 0 to 50% by weight of the ceramic material depending, forexample, upon the desired property.

[0091] In some embodiments, it may be advantageous for at least aportion of a metal oxide source (in some embodiments, preferably, 10 15,20, 25, 30, 35, 40, 45, or even 50, percent by weight) to be obtained byadding particulate, metallic material comprising at least one of a metal(e.g., Al, Ca, Cu, Cr, Fe, Li, Mg, Ni, Ag, Ti, Zr, and combinationsthereof), M, that has a negative enthalpy of oxide formation or an alloythereof to the melt, or otherwise metal them with the other rawmaterials. Although not wanting to be bound by theory, it is believedthat the heat resulting from the exothermic reaction associated with theoxidation of the metal is beneficial in the formation of a homogeneousmelt and resulting amorphous material. For example, it is believed thatthe additional heat generated by the oxidation reaction within the rawmaterial eliminates or minimizes insufficient heat transfer, and hencefacilitates formation and homogeneity of the melt, particularly whenforming amorphous particles with x, y, and z dimensions over 150micrometers. It is also believed that the availability of the additionalheat aids in driving various chemical reactions and physical processes(e.g., densification, and spherodization) to completion. Further, it isbelieved for some embodiments, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation of amelt, which otherwise is difficult or otherwise not practical due tohigh melting point of the materials. Further, the presence of theadditional heat generated by the oxidation reaction actually enables theformation of amorphous material that otherwise could not be made, orcould not be made in the desired size range. Another advantage of theinvention include, in forming the amorphous materials, that many of thechemical and physical processes such as melting, densification andspherodizing can be achieved in a short time, so that very high quenchrates be can achieved. For additional details, see copending applicationhaving U.S. Ser. No. ______ (Attorney Docket No. 56931 US007), filed thesame date as the instant application, the disclosure of which isincorporated herein by reference.

[0092] The addition of certain metal oxides may alter the propertiesand/or crystalline structure or microstructure of ceramics according tothe present invention, as well as the processing of the raw materialsand intermediates in making the ceramic. For example, oxide additionssuch as MgO, CaO, Li₂O, and Na₂O have been observed to alter both theT_(g) and T_(x) (wherein T_(x) is the crystallization temperature) ofglass. Although not wishing to be bound by theory, it is believed thatsuch additions influence glass formation. Further, for example, suchoxide additions may decrease the melting temperature of the overallsystem (i.e., drive the system toward lower melting eutectic), and easeof glass-formation. Complex eutectics in multi component systems(quaternary, etc.) may result in better glass-forming ability. Theviscosity of the liquid melt and viscosity of the glass in its'“working” range may also be affected by the addition of metal oxidesother than Al₂O₃, rare earth oxide(s), and ZrO₂/HfO₂ (such as MgO, CaO,Li₂O, and Na₂O).

[0093] Typically, amorphous materials and the glass-ceramics accordingto the present invention have x, y, and z dimensions each perpendicularto each other, and wherein each of the x, y, and z dimensions is atleast 10 micrometers. In some embodiments, the x, y, and z dimensions isat least 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers,50 micrometers, 75 micrometers, 100 micrometers, 150 micrometers, 200micrometers, 250 micrometers, 500 micrometers, 1000 micrometers, 2000micrometers, 2500 micrometers, 1 mm, 5 mm, or even at least 10 mm. Thex, y, and z dimensions of a material are determined either visually orusing microscopy, depending on the magnitude of the dimensions. Thereported z dimension is, for example, the diameter of a sphere, thethickness of a coating, or the longest length of a prismatic shape.

[0094] Crystallization of amorphous material and ceramic comprising theamorphous material to form glass-ceramics may also be affected by theadditions of materials. For example, certain metals, metal oxides (e.g.,titanates and zirconates), and fluorides, for example, may act asnucleation agents resulting in beneficial heterogeneous nucleation ofcrystals. Also, addition of some oxides may change nature of metastablephases devitrifying from the glass upon reheating. In another aspect,for ceramics according to the present invention comprising crystallineZrO₂, it may be desirable to add metal oxides (e.g., Y₂O₃, TiO₂, CaO,and MgO) that are known to stabilize tetragonal/cubic form of ZrO₂.

[0095] The particular selection of metal oxide sources and otheradditives for making ceramics according to the present inventiontypically takes into account, for example, the desired composition andmicrostructure of the resulting crystalline containing ceramics, thedesired degree of crystallinity, if any, the desired physical properties(e.g., hardness or toughness) of the resulting ceramics, avoiding orminimizing the presence of undesirable impurities, the desiredcharacteristics of the resulting ceramics, and/or the particular process(including equipment and any purification of the raw materials beforeand/or during fusion and/or solidification) being used to prepare theceramics.

[0096] In some instances, it may be preferred to incorporate limitedamounts of metal oxides selected from the group consisting of: Na₂O,P₂O₅, SiO₂, TeO₂, V₂O₃, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides may be added, for example, to modify a physical property of theresulting abrasive particles and/or improve processing. These metaloxides when used are typically are added from greater than 0 to 20% byweight, preferably greater than 0 to 5% by weight and more preferablygreater than 0 to 2% by weight of the glass-ceramic depending, forexample, upon the desired property.

[0097] The metal oxide sources and other additives can be in any formsuitable to the process and equipment being used to make ceramicsaccording to the present invention. The raw materials can be melted andquenched using techniques and equipment known in the art for makingoxide glasses and amorphous metals. Desirable cooling rates includethose of 50K/s and greater. Cooling techniques known in the art includeroll-chilling. Roll-chilling can be carried out, for example, by meltingthe metal oxide sources at a temperature typically 20-200° C. higherthan the melting point, and cooling/quenching the melt by spraying itunder high pressure (e.g., using a gas such as air, argon, nitrogen orthe like) onto a high-speed rotary roll(s). Typically, the rolls aremade of metal and are water cooled. Metal book molds may also be usefulfor cooling/quenching the melt.

[0098] Other techniques for forming melts, cooling/quenching melts,and/or otherwise forming glass include vapor phase quenching, plasmaspraying, melt-extraction, and gas or centrifugal atomization. Vaporphase quenching can be carried out, for example, by sputtering, whereinthe metal alloys or metal oxide sources are formed into a sputteringtarget(s) which are used. The target is fixed at a predeterminedposition in a sputtering apparatus, and a substrate(s) to be coated isplaced at a position opposing the target(s). Typical pressures of 10-3torr of oxygen gas and Ar gas, discharge is generated between thetarget(s) and a substrate(s), and Ar or oxygen ions collide against thetarget to start reaction sputtering, thereby depositing a film ofcomposition on the substrate. For additional details regarding plasmaspraying, see, for example, copending application having U.S. Ser. No.______ (Attorney Docket No. 57980US002), filed the same date as theinstant application, the disclosure of which is incorporated herein byreference.

[0099] Gas atomization involves melting feed particles to convert themto melt. A thin stream of such melt is atomized through contact with adisruptive air jet (i.e., the stream is divided into fine droplets). Theresulting substantially discrete, generally ellipsoidal glass particles(e.g., beads) are then recovered. Examples of bead sizes include thosehaving a diameter in a range of about 5 micrometers to about 3 mm.Melt-extraction can be carried out, for example, as disclosed in U.S.Pat. No. 5,605,870 (Strom-Olsen et al.), the disclosure of which isincorporated herein by reference. Containerless glass forming techniquesutilizing laser beam heating as disclosed, for example, in PCTapplication having Publication No. WO 01/27046 A1, published Apr. 4,2001, the disclosure of which is incorporated herein by reference, mayalso be useful in making glass according to the present invention.

[0100] The cooling rate is believed to affect the properties of thequenched amorphous material. For instance, glass transition temperature,density and other properties of glass typically change with coolingrates.

[0101] Rapid cooling may also be conducted under controlled atmospheres,such as a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence glass formation by influencingcrystallization kinetics from undercooled liquid. For example, largerundercooling of Al₂O₃ melts without crystallization has been reported inargon atmosphere as compared to that in air.

[0102] The microstructure or phase composition(glassy/amorphous/crystalline) of a material can be determined in anumber of ways. Various information can be obtained using opticalmicroscopy, electron microscopy, differential thermal analysis (DTA),and x-ray diffraction (XRD), for example.

[0103] Using optical microscopy, amorphous material is typicallypredominantly transparent due to the lack of light scattering centerssuch as crystal boundaries, while crystalline material shows acrystalline structure and is opaque due to light scattering effects.

[0104] A percent amorphous yield can be calculated for beads using a−100+120 mesh size fraction (i.e., the fraction collected between150-micrometer opening size and 125-micrometer opening size screens).The measurements are done in the following manner. A single layer ofbeads is spread out upon a glass slide. The beads are observed using anoptical microscope. Using the crosshairs in the optical microscopeeyepiece as a guide, beads that lay along a straight line are countedeither amorphous or crystalline depending on their optical clarity. Atotal of 500 beads are counted and a percent amorphous yield isdetermined by the amount of amorphous beads divided by total beadscounted.

[0105] Using DTA, the material is classified as amorphous if thecorresponding DTA trace of the material contains an exothermiccrystallization event (T_(x)). If the same trace also contains anendothermic event (T_(g)) at a temperature lower than T_(x) it isconsidered to consist of a glass phase. If the DTA trace of the materialcontains no such events, it is considered to contain crystalline phases.

[0106] Differential thermal analysis (DTA) can be conducted using thefollowing method. DTA runs can be made (using an instrument such as thatobtained from Netzsch Instruments, Selb, Germany under the tradedesignation “NETZSCH STA 409 DTA/TGA”) using a −140+170 mesh sizefraction (i.e., the fraction collected between 105-micrometer openingsize and 90-micrometer opening size screens). An amount of each screenedsample (typically about 400 milligrams (mg)) is placed in a100-microliter Al₂O₃ sample holder. Each sample is heated in static airat a rate of 10° C./minute from room temperature (about 25° C.) to 1100°C.

[0107] Using powder x-ray diffraction, XRD, (using an x-raydiffractometer such as that obtained under the trade designation“PHILLIPS XRG 3100” from Phillips, Mahwah, N.J., with copper K α1radiation of 1.54050 Angstrom) the phases present in a material can bedetermined by comparing the peaks present in the XRD trace of thecrystallized material to XRD patterns of crystalline phases provided inJCPDS (Joint Committee on Powder Diffraction Standards) databases,published by International Center for Diffraction Data. Furthermore, anXRD can be used qualitatively to determine types of phases. The presenceof a broad diffused intensity peak is taken as an indication of theamorphous nature of a material. The existence of both a broad peak andwell-defined peaks is taken as an indication of existence of crystallinematter within an amorphous matrix. The initially formed amorphousmaterial or ceramic (including glass prior to crystallization) may belarger in size than that desired. The amorphous material or ceramic canbe converted into smaller pieces using crushing and/or comminutingtechniques known in the art, including roll crushing, canary milling,jaw crushing, hammer milling, ball milling, jet milling, impactcrushing, and the like. In some instances, it is desired to have two ormultiple crushing steps. For example, after the ceramic is formed(solidified), it may be in the form of larger than desired. The firstcrushing step may involve crushing these relatively large masses or“chunks” to form smaller pieces. This crushing of these chunks may beaccomplished with a hammer mill, impact crusher or jaw crusher. Thesesmaller pieces may then be subsequently crushed to produce the desiredparticle size distribution. In order to produce the desired particlesize distribution (sometimes referred to as grit size or grade), it maybe necessary to perform multiple crushing steps. In general the crushingconditions are optimized to achieve the desired particle shape(s) andparticle size distribution. Resulting particles that are of the desiredsize may be recrushed if they are too large, or “recycled” and used as araw material for re-melting if they are too small.

[0108] The shape of particles can depend, for example, on thecomposition and/or microstructure of the ceramic, the geometry in whichit was cooled, and the manner in which the ceramic is crushed (i.e., thecrushing technique used). In general, where a “blocky” shape ispreferred, more energy may be employed to achieve this shape.Conversely, where a “sharp” shape is preferred, less energy may beemployed to achieve this shape. The crushing technique may also bechanged to achieve different desired shapes. For some particles anaverage aspect ratio ranging from 1:1 to 5:1 is typically desired, andin some embodiments 1.25:1 to 3:1, or even 1.5:1 to 2.5:1.

[0109] It is also within the scope of the present invention, forexample, to directly form articles in desired shapes. For example,desired articles may be formed (including molded) by pouring or formingthe melt into a mold.

[0110] Surprisingly, it was found that ceramics of present inventioncould be obtained without limitations in dimensions. This was found tobe possible through a coalescing step performed at temperatures aboveglass transition temperature. This coalescing step in essence forms alarger sized body from two or more smaller particles. For instance, asevident from FIG. 7, glass of present invention undergoes glasstransition (T_(g)) before significant crystallization occurs (T_(g)) asevidenced by the existence of endotherm (T_(g)) at lower temperaturethan exotherm (T_(x)). For example, ceramic (including glass prior tocrystallization), may also be provided by heating, for example,particles comprising the amorphous material, and/or fibers, etc. abovethe T_(g) such that the particles, etc. coalesce to form a shape andcooling the coalesced shape. The temperature and pressure used forcoalescing may depend, for example, upon composition of the amorphousmaterial and the desired density of the resulting material. For glassestemperature should be greater than the glass transition temperature. Incertain embodiments, the heating is conducted at at least onetemperature in a range of about 850° C. to about 1100° C. (in someembodiments, preferably 900° C. to 1000° C.). Typically, the amorphousmaterial is under pressure (e.g., greater than zero to 1 GPa or more)during coalescence to aid the coalescence of the amorphous material. Inone embodiment, a charge of the particles, etc. is placed into a die andhot-pressing is performed at temperatures above glass transition whereviscous flow of glass leads to coalescence into a relatively large part.Examples of typical coalescing techniques include hot pressing, hotisostatic pressure, hot extrusion and the like. For example, amorphousmaterial comprising particles (obtained, for example, by crushing)(including beads and microspheres), fibers, etc. may formed into alarger particle size. Typically, it is generally preferred to cool theresulting coalesced body before further heat treatment. After heattreatment if so desired, the coalesced body may be crushed to smallerparticle sizes or a desired particle size distribution.

[0111] It is also within the scope of the present invention to conductadditional heat-treatment to further improve desirable properties of thematerial. For example, hot-isostatic pressing may be conducted (e.g., attemperatures from about 900° C. to about 1400° C.) to remove residualporosity, increasing the density of the material. Optionally, theresulting, coalesced article can be heat-treated to provideglass-ceramic, crystalline ceramic, or ceramic otherwise comprisingcrystalline ceramic.

[0112] Coalescing of the amorphous material and/or glass-ceramic (e.g.,particles) may also be accomplished by a variety of methods, includingpressureless or pressure sintering (e.g., sintering, plasma assistedsintering, hot pressing, HIPing, hot forging, hot extrusion, etc.).

[0113] Heat-treatment can be carried out in any of a variety of ways,including those known in the art for heat-treating glass to provideglass-ceramics. For example, heat-treatment can be conducted in batches,for example, using resistive, inductively or gas heated furnaces.Alternatively, for example, heat-treatment can be conductedcontinuously, for example, using rotary kilns. In the case of a rotarykiln, the material is fed directly into a kiln operating at the elevatedtemperature. The time at the elevated temperature may range from a fewseconds (in some embodiments even less than 5 seconds) to a few minutesto several hours. The temperature may range anywhere from 900° C. to1600° C., typically between 1200° C. to 1500° C. It is also within thescope of the present invention to perform some of the heat-treatment inbatches (e.g., for the nucleation step) and another continuously (e.g.,for the crystal growth step and to achieve the desired density). For thenucleation step, the temperature typically ranges between about 900° C.to about 1100° C., in some embodiments, preferably in a range from about925° C. to about 1050° C. Likewise for the density step, the temperaturetypically is in a range from about 1100° C. to about 1600° C., in someembodiments, preferably in a range from about 1200° C. to about 1500° C.This heat treatment may occur, for example, by feeding the materialdirectly into a furnace at the elevated temperature. Alternatively, forexample, the material may be feed into a furnace at a much lowertemperature (e.g., room temperature) and then heated to desiredtemperature at a predetermined heating rate. It is within the scope ofthe present invention to conduct heat-treatment in an atmosphere otherthan air. In some cases it might be even desirable to heat-treat in areducing atmosphere(s). Also, for, example, it may be desirable toheat-treat under gas pressure as in, for example, hot-isostatic press,or in gas pressure furnace. It is within the scope of the presentinvention to convert (e.g., crush) the resulting article or heat-treatedarticle to provide particles (e.g., abrasive particles).

[0114] The amorphous material is heat-treated to at least partiallycrystallize the amorphous material to provide glass-ceramic. Theheat-treatment of certain glasses to form glass-ceramics is well knownin the art. The heating conditions to nucleate and grow glass-ceramicsare known for a variety of glasses. Alternatively, one skilled in theart can determine the appropriate conditions from aTime-Temperature-Transformation (TTT) study of the glass usingtechniques known in the art. One skilled in the art, after reading thedisclosure of the present invention should be able to provide TTT curvesfor glasses according to the present invention, determine theappropriate nucleation and/or crystal growth conditions to provideglass-ceramics according to the present invention.

[0115] Typically, glass-ceramics are stronger than the amorphousmaterials from which they are formed. Hence, the strength of thematerial may be adjusted, for example, by the degree to which theamorphous material is converted to crystalline ceramic phase(s).Alternatively, or in addition, the strength of the material may also beaffected, for example, by the number of nucleation sites created, whichmay in turn be used to affect the number, and in turn the size of thecrystals of the crystalline phase(s). For additional details regardingforming glass-ceramics, see, for example Glass-Ceramics, P. W. McMillan,Academic Press, Inc., 2^(nd) edition, 1979, the disclosure of which isincorporated herein by reference.

[0116] For example, during heat-treatment of some exemplary amorphousmaterials for making glass-ceramics according to present invention,formation of phases such as La₂Zr₂O₇, and, if ZrO₂ is present,cubic/tetragonal ZrO₂, in some cases monoclinic ZrO₂, have been observedat temperatures above about 900° C. Although not wanting to be bound bytheory, it is believed that zirconia-related phases are the first phasesto nucleate from the amorphous material. Formation of Al₂O₃, ReAlO₃(wherein Re is at least one rare earth cation), ReAl₁₁O₁₈, Re₃Al₅O₁₂,Y₃Al₅O₁₂, etc. phases are believed to generally occur at temperaturesabove about 925° C. Typically, crystallite size during this nucleationstep is on order of nanometers. For example, crystals as small as 10-15nanometers have been observed. For at least some embodiments,heat-treatment at about 1300° C. for about 1 hour provides a fullcrystallization. In generally, heat-treatment times for each of thenucleation and crystal growth steps may range of a few seconds (in someembodiments even less than 5 seconds) to several minutes to an hour ormore.

[0117] Examples of crystalline phases which may be present in ceramicsaccording to the present invention include: complex Al₂O₃.metal oxide(s)(e.g., complex Al₂O₃.REO (e.g., ReAlO₃ (e.g., GdAlO₃ LaAlO₃), ReAl₁₁O₁₈(e.g., LaAl₁₁O₁₈,), and Re₃Al₅O₁₂ (e.g., Dy₃Al₅O₁₂)), complex Al₂O₃.Y₂O₃(e.g., Y₃Al₅O₁₂), and complex ZrO₂.REO (e.g., La₂Zr₂O₇)), Al₂O₃ (e.g.,α-Al₂O₃), and ZrO₂ (e.g., cubic ZrO₂ and tetragonal ZrO₂).

[0118] It is also with in the scope of the present invention tosubstitute a portion of the yttrium and/or aluminum cations in a complexAl₂O₃.metal oxide (e.g., complex Al₂O₃.Y₂O₃ (e.g., yttrium aluminateexhibiting a garnet crystal structure)) with other cations. For example,a portion of the Al cations in a complex Al₂O₃.Y₂O₃ may be substitutedwith at least one cation of an element selected from the groupconsisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinations thereof.For example, a portion of the Y cations in a complex Al₂O₃.Y₂O₃ may besubstituted with at least one cation of an element selected from thegroup consisting of: Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Th, Tm,Yb, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr, and combinations thereof.Similarly, it is also with in the scope of the present invention tosubstitute a portion of the aluminum cations in alumina. For example,Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitute for aluminum in thealumina. The substitution of cations as described above may affect theproperties (e.g. hardness, toughness, strength, thermal conductivity,etc.) of the fused material.

[0119] It is also with in the scope of the present invention tosubstitute a portion of the rare earth and/or aluminum cations in acomplex Al₂O₃.metal oxide (e.g., complex Al₂O₃.REO) with other cations.For example, a portion of the Al cations in a complex Al₂O₃.REO may besubstituted with at least one cation of an element selected from thegroup consisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinationsthereof. For example, a portion of the Y cations in a complex Al₂O₃.REOmay be substituted with at least one cation of an element selected fromthe group consisting of: Y, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr,and combinations thereof. Similarly, it is also with in the scope of thepresent invention to substitute a portion of the aluminum cations inalumina. For example, Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitutefor aluminum in the alumina. The substitution of cations as describedabove may affect the properties (e.g. hardness, toughness, strength,thermal conductivity, etc.) of the fused material.

[0120] The average crystal size can be determined by the line interceptmethod according to the ASTM standard E 112-96 “Standard Test Methodsfor Determining Average Grain Size”. The sample is mounted in mountingresin (such as that obtained under the trade designation “TRANSOPTICPOWDER” from Buehler, Lake Bluff, Ill.) typically in a cylinder of resinabout 2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The mounted and polished sample issputtered with a thin layer of gold-palladium and viewed using ascanning electron microscopy (such as the JEOL SEM Model JSM 840A). Atypical back-scattered electron (BSE) micrograph of the microstructurefound in the sample is used to determine the average crystal size asfollows. The number of crystals that intersect per unit length (NL) of arandom straight line drawn across the micrograph are counted. Theaverage crystal size is determined from this number using the followingequation.${{Average}\quad {Crystal}\quad {Size}} = \frac{1.5}{N_{L}M}$

[0121] Where N_(L) is the number of crystals intersected per unit lengthand M is the magnification of the micrograph.

[0122] In another aspect, ceramics (including glass-ceramics) accordingto the present invention may comprise at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystallites, wherein the crystalliteshave an average size of less than 1 micrometer. In another aspect,ceramics (including glass-ceramics) according to the present inventionmay comprise less than at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystallites, wherein the crystallites have an averagesize of less than 0.5 micrometer. In another aspect, ceramics (includingglass-ceramics) according to the present invention may comprise lessthan at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60,65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystallites, wherein the crystallites have an average size of less than0.3 micrometer. In another aspect, ceramics (including glass-ceramics)according to the present invention may comprise less than at least 1, 2,3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 97, 98, 99, or even 100 percent by volume crystallites, whereinthe crystallites have an average size of less than 0.15 micrometer.

[0123] Crystalline phases that may be present in ceramics according tothe present invention include alumina (e.g., alpha and transitionaluminas), REO, HfO₂ ZrO₂, as well as, for example, one or more othermetal oxides such as BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO,NiO, Na₂O, P₂O₅, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, “complexmetal oxides” (including complex Al₂O₃-metal oxide (e.g., complexAl₂O₃.REO)), and combinations thereof.

[0124] Additional details regarding ceramics comprising Al₂O₃, Y₂O₃, andat least one of ZrO₂ or HfO₂, including making, using, and properties,can be found in application having U.S. Ser. Nos. 09/922,526,09/922,528, and 09/922,530, filed Aug. 2, 2001, and U.S. Ser. No. ______(Attorney Docket Nos. 56931US005, 56931US006, 56931US007, 56931US008,56931US009, 56931US010, 57980US002, and 57981US002, filed the same dateas the instant application, the disclosures of which are incorporatedherein by reference.

[0125] Crystals formed by heat-treating amorphous to provide embodimentsof glass-ceramics according to the present invention may be, forexample, acicular equiaxed, columnar, or flattened splat-like features.

[0126] Although an amorphous material, glass-ceramic, etc. according tothe present invention may be in the form of a bulk material, it is alsowithin the scope of the present invention to provide compositescomprising an amorphous material, glass-ceramic, etc. according to thepresent invention. Such a composite may comprise, for example, a phaseor fibers (continuous or discontinuous) or particles (includingwhiskers) (e.g., metal oxide particles, boride particles, carbideparticles, nitride particles, diamond particles, metallic particles,glass particles, and combinations thereof) dispersed in an amorphousmaterial, glass-ceramic, etc. according to the present invention,invention or a layered-composite structure (e.g., a gradient ofglass-ceramic to amorphous material used to make the glass-ceramicand/or layers of different compositions of glass-ceramics).

[0127] Certain glasses according to the present invention may have, forexample, a T_(g) in a range of about 750° C. to about 860° C. Certainglasses according to the present invention may have, for example, aYoung's modulus in a range of about 110 GPa to at least about 150 GPa,crystalline ceramics according to the present invention from about 200GPa to at least about 300 GPa, and glass-ceramics according to thepresent invention or ceramics according to the present inventioncomprising glass and crystalline ceramic from about 110 GPa to about 250GPa. Certain glasses according to the present invention may have, forexample, an average toughness (i.e., resistance to fracture) in a rangeof about 1 MPa*m^(1/2) to about 3 MPa*m^(1/2), crystalline ceramicsaccording to the present invention from about 3 MPa*m^(1/2) to about 5MPa*m^(1/2), and glass-ceramics according to the present invention orceramics according to the present invention comprising glass andcrystalline ceramic from about 1 MPa*m^(1/2) to about 5 MPa*m^(1/2).

[0128] The average hardness of the material of the present invention canbe determined as follows. Sections of the material are mounted inmounting resin (obtained under the trade designation “TRANSOPTIC POWDER”from Buehler, Lake Bluff, Ill.) typically in a cylinder of resin about2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The microhardness measurements aremade using a conventional microhardness tester (such as that obtainedunder the trade designation “MITUTOYO MVK-VL” from Mitutoyo Corporation,Tokyo, Japan) fitted with a Vickers indenter using a 100-gram indentload. The microhardness measurements are made according to theguidelines stated in ASTM Test Method E384 Test Methods forMicrohardness of Materials (1991), the disclosure of which isincorporated herein by reference.

[0129] Certain glasses according to the present invention may have, forexample, an average hardness of at least 5 GPa (more desirably, at least6 GPa, 7 GPa, 8 GPa, or 9 GPa; typically in a range of about 5 GPa toabout 10 GPa), crystalline ceramics according to the present inventionat least 5 GPa (more desirably, at least 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, or 18 GPa;typically in a range of about 5 GPa to about 18 GPa), and glass-ceramicsaccording to the present invention or ceramics according to the presentinvention comprising glass and crystalline ceramic at least 5 GPa (moredesirably, at least 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, 11 GPa, 12 GPa,13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, or 18 GPa (or more); typicallyin a range of about 5 GPa to about 18 GPa). Abrasive particles accordingto the present invention have an average hardness of at least 15 GPa, insome embodiments, preferably, at least 16 GPa, at least 17 GPa, or evenat least 18 GPa.

[0130] Certain glasses according to the present invention may have, forexample, a thermal expansion coefficient in a range of about 5×10⁻⁶/K toabout 11×10⁻⁶/K over a temperature range of at least 25° C. to about900° C.

[0131] Typically, and desirably, the (true) density, sometimes referredto as specific gravity, of ceramic according to the present invention istypically at least 70% of theoretical density. More desirably, the(true) density of ceramic according to the present invention is at least75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5% or even 100% oftheoretical density. Abrasive particles according to the presentinvention have densities of at least 85%, 90%, 92%, 95%, 96%, 97%, 98%,99%, 99.5% or even 100% of theoretical density.

[0132] Articles can be made using ceramics according to the presentinvention, for example, as a filler, reinforcement material, and/ormatrix material. For example, ceramic according to the present inventioncan be in the form of particles and/or fibers suitable for use asreinforcing materials in composites (e.g., ceramic, metal, or polymeric(thermosetting or thermoplastic). The particles and/or fibers may, forexample, increase the modulus, heat resistance, wear resistance, and/orstrength of the matrix material. Although the size, shape, and amount ofthe particles and/or fibers used to make a composite may depend, forexample, on the particular matrix material and use of the composite, thesize of the reinforcing particles typically range about 0.1 to 1500micrometers, more typically 1 to 500 micrometers, and desirably between2 to 100 micrometers. The amount of particles for polymeric applicationsis typically about 0.5 percent to about 75 percent by weight, moretypically about 1 to about 50 percent by weight. Examples ofthermosetting polymers include: phenolic, melamine, urea formaldehyde,acrylate, epoxy, urethane polymers, and the like. Examples ofthermoplastic polymers include: nylon, polyethylene, polypropylene,polyurethane, polyester, polyamides, and the like.

[0133] Examples of uses for reinforced polymeric materials (i.e.,reinforcing particles according to the present invention dispersed in apolymer) include protective coatings, for example, for concrete,furniture, floors, roadways, wood, wood-like materials, ceramics, andthe like, as well as, anti-skid coatings and injection molded plasticparts and components.

[0134] Further, for example, ceramic according to the present inventioncan be used as a matrix material. For example, ceramics according to thepresent invention can be used as a binder for ceramic materials and thelike such as diamond, cubic-BN, Al₂O₃, ZrO₂, Si₃N₄, and SiC. Examples ofuseful articles comprising such materials include composite substratecoatings, cutting tool inserts abrasive agglomerates, and bondedabrasive articles such as vitrified wheels. The use of ceramicsaccording to the present invention can be used as binders may, forexample, increase the modulus, heat resistance, wear resistance, and/orstrength of the composite article.

[0135] Abrasive particles according to the present invention generallycomprise crystalline ceramic (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, or even 100 percent by volume) crystallineceramic. In another aspect, the present invention provides a pluralityof particles having a particle size distribution ranging from fine tocoarse, wherein at least a portion of the plurality of particles areabrasive particles according to the present invention. In anotheraspect, embodiments of abrasive particles according to the presentinvention generally comprise (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, or even 100 percent by volume)glass-ceramic according to the present invention.

[0136] Abrasive particles according to the present invention can bescreened and graded using techniques well known in the art, includingthe use of industry recognized grading standards such as ANSI (AmericanNational Standard Institute), FEPA (Federation Europeenne des Fabricantsde Products Abrasifs), and JIS (Japanese Industrial Standard). Abrasiveparticles according to the present invention may be used in a wide rangeof particle sizes, typically ranging in size from about 0.1 to about5000 micrometers, more typically from about 1 to about 2000 micrometers;desirably from about 5 to about 1500 micrometers, more desirably fromabout 100 to about 1500 micrometers.

[0137] In a given particle size distribution, there will be a range ofparticle sizes, from coarse particles fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards include those known as the American National StandardsInstitute, Inc. (ANSI) standards, Federation of European Producers ofAbrasive Products (FEPA) standards, and Japanese Industrial Standard(JIS) standards. ANSI grade designations (i.e., specified nominalgrades) include: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI40, ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI 120, ANSI 150, ANSI 180,ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, and ANSI600. Preferred ANSI grades comprising abrasive particles according tothe present invention are ANSI 8-220. FEPA grade designations includeP8, P12, P16, P24, P36, P40, P50, P60, P80, P100, P120, P150, P180,P220, P320, P400, P500, P600, P800, P1000, and P1200. Preferred FEPAgrades comprising abrasive particles according to the present inventionare P12-P220. JIS grade designations include JIS8, JIS12, JIS16, JIS24,JIS36, JIS46, JIS54, JIS60, JIS80, JIS100, JIS150, JIS180, JIS220,JIS240, JIS280, JIS320, JIS360, JIS400, JIS400, JIS600, JIS800, JIS1000,JIS 1500, JIS2500, JIS4000, JIS6000, JIS8000, and JIS 10,000. PreferredJIS grades comprising abrasive particles according to the presentinvention are JIS8-220.

[0138] After crushing and screening, there will typically be a multitudeof different abrasive particle size distributions or grades. Thesemultitudes of grades may not match a manufacturer's or supplier's needsat that particular time. To minimize inventory, it is possible torecycle the off demand grades back into melt to form glass. Thisrecycling may occur after the crushing step, where the particles are inlarge chunks or smaller pieces (sometimes referred to as “fines”) thathave not been screened to a particular distribution.

[0139] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising heat-treating glassparticles or glass-containing particles according to the presentinvention to provide abrasive particles comprising a glass-ceramicaccording to the present invention. Alternatively, for example, thepresent invention provides a method for making abrasive particles, themethod comprising heat-treating glass according to the presentinvention, and crushing the resulting heat-treated material to provideabrasive particles comprising a glass-ceramic according to the presentinvention. When crushed, glass tends to provide sharper particles thancrushing significantly crystallized glass-ceramics or crystallinematerial.

[0140] In another aspect, the present invention provides agglomerateabrasive grains each comprising a plurality of abrasive particlesaccording to the present invention bonded together via a binder. Inanother aspect, the present invention provides an abrasive article(e.g., coated abrasive articles, bonded abrasive articles (includingvitrified, resinoid, and metal bonded grinding wheels, cutoff wheels,mounted points, and honing stones), nonwoven abrasive articles, andabrasive brushes) comprising a binder and a plurality of abrasiveparticles, wherein at least a portion of the abrasive particles areabrasive particles (including where the abrasive particles areagglomerated) according to the present invention. Methods of making suchabrasive articles and using abrasive articles are well known to thoseskilled in the art. Furthermore, abrasive particles according to thepresent invention can be used in abrasive applications that utilizeabrasive particles, such as slurries of abrading compounds (e.g.,polishing compounds), milling media, shot blast media, vibratory millmedia, and the like.

[0141] Coated abrasive articles generally include a backing, abrasiveparticles, and at least one binder to hold the abrasive particles ontothe backing. The backing can be any suitable material, including cloth,polymeric film, fibre, nonwoven webs, paper, combinations thereof, andtreated versions thereof. The binder can be any suitable binder,including an inorganic or organic binder (including thermally curableresins and radiation curable resins). The abrasive particles can bepresent in one layer or in two layers of the coated abrasive article.

[0142] An example of a coated abrasive article is depicted in FIG. 9.Referring to this figure, coated abrasive article 1 has a backing(substrate) 2 and abrasive layer 3. Abrasive layer 3 includes abrasiveparticles according to the present invention 4 secured to a majorsurface of backing 2 by make coat 5 and size coat 6. In some instances,a supersize coat (not shown) is used.

[0143] Bonded abrasive articles typically include a shaped mass ofabrasive particles held together by an organic, metallic, or vitrifiedbinder. Such shaped mass can be, for example, in the form of a wheel,such as a grinding wheel or cutoff wheel. The diameter of grindingwheels typically is about 1 cm to over 1 meter; the diameter of cut offwheels about 1 cm to over 80 cm (more typically 3 cm to about 50 cm).The cut off wheel thickness is typically about 0.5 mm to about 5 cm,more typically about 0.5 mm to about 2 cm. The shaped mass can also bein the form, for example, of a honing stone, segment, mounted point,disc (e.g. double disc grinder) or other conventional bonded abrasiveshape. Bonded abrasive articles typically comprise about 3-50% by volumebond material, about 30-90% by volume abrasive particles (or abrasiveparticle blends), up to 50% by volume additives (including grindingaids), and up to 70% by volume pores, based on the total volume of thebonded abrasive article.

[0144] A preferred form is a grinding wheel. Referring to FIG. 10,grinding wheel 10 is depicted, which includes abrasive particlesaccording to the present invention 11, molded in a wheel and mounted onhub 12.

[0145] Nonwoven abrasive articles typically include an open porous loftypolymer filament structure having abrasive particles according to thepresent invention distributed throughout the structure and adherentlybonded therein by an organic binder. Examples of filaments includepolyester fibers, polyamide fibers, and polyaramid fibers. In FIG. 11, aschematic depiction, enlarged about 100×, of a typical nonwoven abrasivearticle is provided. Such a nonwoven abrasive article comprises fibrousmat 50 as a substrate, onto which abrasive particles according to thepresent invention 52 are adhered by binder 54.

[0146] Useful abrasive brushes include those having a plurality ofbristles unitary with a backing (see, e.g., U.S. Pat. Nos. 5,427,595(Pihl et al.), 5,443,906 (Pihl et al.), 5,679,067 (Johnson et al.), and5,903,951 (lonta et al.), the disclosure of which is incorporated hereinby reference). Desirably, such brushes are made by injection molding amixture of polymer and abrasive particles.

[0147] Suitable organic binders for making abrasive articles includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive article may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents(e.g., silanes, titanates, zircoaluminates, etc.), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the abrasive particles and/or filler. The binderchemistry may thermally cured, radiation cured or combinations thereof.Additional details on binder chemistry may be found in U.S. Pat. Nos.4,588,419 (Caul et al.), 4,751,138 (Tumey et al.), and 5,436,063(Follett et al.), the disclosures of which are incorporated herein byreference.

[0148] More specifically with regard to vitrified bonded abrasives,vitreous bonding materials, which exhibit an amorphous structure and aretypically hard, are well known in the art. In some cases, the vitreousbonding material includes crystalline phases. Bonded, vitrified abrasivearticles according to the present invention may be in the shape of awheel (including cut off wheels), honing stone, mounted pointed or otherconventional bonded abrasive shape. A preferred vitrified bondedabrasive article according to the present invention is a grinding wheel.

[0149] Examples of metal oxides that are used to form vitreous bondingmaterials include: silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate,combinations thereof, and the like. Typically, vitreous bondingmaterials can be formed from composition comprising from 10 to 100%glass frit, although more typically the composition comprises 20% to 80%glass frit, or 30% to 70% glass frit. The remaining portion of thevitreous bonding material can be a non-frit material. Alternatively, thevitreous bond may be derived from a non-frit containing composition.Vitreous bonding materials are typically matured at a temperature(s) ina range of about 700° C. to about 1500° C., usually in a range of about800° C. to about 1300° C., sometimes in a range of about 900° C. toabout 1200° C., or even in a range of about 950° C. to about 1100° C.The actual temperature at which the bond is matured depends, forexample, on the particular bond chemistry.

[0150] Preferred vitrified bonding materials may include thosecomprising silica, alumina (desirably, at least 10 percent by weightalumina), and boria (desirably, at least 10 percent by weight boria). Inmost cases the vitrified bonding material further comprise alkali metaloxide(s) (e.g., Na₂O and K₂O) (in some cases at least 10 percent byweight alkali metal oxide(s)).

[0151] Binder materials may also contain filler materials or grindingaids, typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers for this invention include: metal carbonates (e.g., calciumcarbonate (e.g., chalk, calcite, marl, travertine, marble andlimestone), calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate), silica (e.g., quartz, glass beads, glass bubbles and glassfibers) silicates (e.g., talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate) metal sulfates (e.g., calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides(e.g., calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (e.g., calcium sulfite).

[0152] In general, the addition of a grinding aid increases the usefullife of the abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance. Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive particles and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

[0153] Grinding aids encompass a wide variety of different materials andcan be inorganic or organic based. Examples of chemical groups ofgrinding aids include waxes, organic halide compounds, halide salts andmetals and their alloys. The organic halide compounds will typicallybreak down during abrading and release a halogen acid or a gaseoushalide compound. Examples of such materials include chlorinated waxeslike tetrachloronaphtalene, pentachloronaphthalene, and polyvinylchloride. Examples of halide salts include sodium chloride, potassiumcryolite, sodium cryolite, ammonium cryolite, potassiumtetrafluoroboate, sodium tetrafluoroborate, silicon fluorides, potassiumchloride, and magnesium chloride. Examples of metals include, tin, lead,bismuth, cobalt, antimony, cadmium, and iron titanium. Othermiscellaneous grinding aids include sulfur, organic sulfur compounds,graphite, and metallic sulfides. It is also within the scope of thepresent invention to use a combination of different grinding aids, andin some instances this may produce a synergistic effect. The preferredgrinding aid is cryolite; the most preferred grinding aid is potassiumtetrafluoroborate.

[0154] Grinding aids can be particularly useful in coated abrasive andbonded abrasive articles. In coated abrasive articles, grinding aid istypically used in the supersize coat, which is applied over the surfaceof the abrasive particles. Sometimes, however, the grinding aid is addedto the size coat. Typically, the amount of grinding aid incorporatedinto coated abrasive articles are about 50-300 g/m² (desirably, about80-160 g/m²). In vitrified bonded abrasive articles grinding aid istypically impregnated into the pores of the article.

[0155] The abrasive articles can contain 100% abrasive particlesaccording to the present invention, or blends of such abrasive particleswith other abrasive particles and/or diluent particles. However, atleast about 2% by weight, desirably at least about 5% by weight, andmore desirably about 30-100% by weight, of the abrasive particles in theabrasive articles should be abrasive particles according to the presentinvention. In some instances, the abrasive particles according thepresent invention may be blended with another abrasive particles and/ordiluent particles at a ratio between 5 to 75% by weight, about 25 to 75%by weight about 40 to 60% by weight, or about 50% to 50% by weight(i.e., in equal amounts by weight). Examples of suitable conventionalabrasive particles include fused aluminum oxide (including white fusedalumina, heat-treated aluminum oxide and brown aluminum oxide), siliconcarbide, boron carbide, titanium carbide, diamond, cubic boron nitride,garnet, fused alumina-zirconia, and sol-gel-derived abrasive particles,and the like. The sol-gel-derived abrasive particles may be seeded ornon-seeded. Likewise, the sol-gel-derived abrasive particles may berandomly shaped or have a shape associated with them, such as a rod or atriangle. Examples of sol gel abrasive particles include those describedU.S. Pat. Nos. 4,314,827 (Leitheiser et al.), 4,518,397 (Leitheiser etal.), 4,623,364 (Cottringer et al.), 4,744,802 (Schwabel), 4,770,671(Monroe et al.), 4,881,951 (Wood et al.), 5,011,508 (Wald et al.),5,090,968 (Pellow), 5,139,978 (Wood), 5,201,916 (Berg et al.), 5,227,104(Bauer), 5,366,523 (Rowenhorst et al.), 5,429,647 (Larmie), 5,498,269(Larmie), and 5,551,963 (Larmie), the disclosures of which areincorporated herein by reference. Additional details concerning sinteredalumina abrasive particles made by using alumina powders as a rawmaterial source can also be found, for example, in U.S. Pat. Nos.5,259,147 (Falz), 5,593,467 (Monroe), and 5,665,127 (Moltgen), thedisclosures of which are incorporated herein by reference. Additionaldetails concerning fused abrasive particles, can be found, for example,in U.S. Pat. Nos. 1,161,620 (Coulter), 1,192,709 (Tone), 1,247,337(Saunders et al.), 1,268,533 (Allen), and 2,424,645 (Baumann et al.)3,891,408 (Rowse et al.), 3,781,172 (Pett et al.), 3,893,826 (Quinan etal.), 4,126,429 (Watson), 4,457,767 (Poon et al.), 5,023,212 (Dubots et.al), 5,143,522 (Gibson et al.), and 5,336,280 (Dubots et. al), andapplications having U.S. Serial Nos. 09,495,978, 09/496,422, 09/496,638,and 09/496,713, each filed on Feb. 2, 2000, and, 09/618,876, 09/618,879,09/619,106, 09/619,191, 09/619,192, 09/619,215, 09/619,289, 09/619,563,09/619,729, 09/619,744, and 09/620,262, each filed on Jul. 19, 2000, andSer. No. 09/772,730, filed Jan. 30, 2001, the disclosures of which areincorporated herein by reference. In some instances, blends of abrasiveparticles may result in an abrasive article that exhibits improvedgrinding performance in comparison with abrasive articles comprising100% of either type of abrasive particle.

[0156] If there is a blend of abrasive particles, the abrasive particletypes forming the blend may be of the same size. Alternatively, theabrasive particle types may be of different particle sizes. For example,the larger sized abrasive particles may be abrasive particles accordingto the present invention, with the smaller sized particles being anotherabrasive particle type. Conversely, for example, the smaller sizedabrasive particles may be abrasive particles according to the presentinvention, with the larger sized particles being another abrasiveparticle type.

[0157] Examples of suitable diluent particles include marble, gypsum,flint, silica, iron oxide, aluminum silicate, glass (including glassbubbles and glass beads), alumina bubbles, alumina beads and diluentagglomerates. Abrasive particles according to the present invention canalso be combined in or with abrasive agglomerates. Abrasive agglomerateparticles typically comprise a plurality of abrasive particles, abinder, and optional additives. The binder may be organic and/orinorganic. Abrasive agglomerates may be randomly shape or have apredetermined shape associated with them. The shape may be a block,cylinder, pyramid, coin, square, or the like. Abrasive agglomerateparticles typically have particle sizes ranging from about 100 to about5000 micrometers, typically about 250 to about 2500 micrometers.Additional details regarding abrasive agglomerate particles may befound, for example, in U.S. Pat. Nos. 4,311,489 (Kressner), 4,652,275(Bloecher et al.), 4,799,939 (Bloecher et al.), 5,549,962 (Holmes etal.), and 5,975,988 (Christianson), and applications having U.S. Ser.Nos. 09/688,444 and 09/688,484, filed Oct. 16, 2000, the disclosures ofwhich are incorporated herein by reference.

[0158] The abrasive particles may be uniformly distributed in theabrasive article or concentrated in selected areas or portions of theabrasive article. For example, in a coated abrasive, there may be twolayers of abrasive particles. The first layer comprises abrasiveparticles other than abrasive particles according to the presentinvention, and the second (outermost) layer comprises abrasive particlesaccording to the present invention. Likewise in a bonded abrasive, theremay be two distinct sections of the grinding wheel. The outermostsection may comprise abrasive particles according to the presentinvention, whereas the innermost section does not. Alternatively,abrasive particles according to the present invention may be uniformlydistributed throughout the bonded abrasive article.

[0159] Further details regarding coated abrasive articles can be found,for example, in U.S. Pat. Nos. 4,734,104 (Broberg), 4,737,163 (Larkey),5,203,884 (Buchanan et al.), 5,152,917 (Pieper et al.), 5,378,251(Culler et al.), 5,417,726 (Stout et al.), 5,436,063 (Follett et al.),5,496,386 (Broberg et al.), 5, 609,706 (Benedict et al.), 5,520,711(Helmin), 5,954,844 (Law et al.), 5,961,674 (Gagliardi et al.), and5,975,988 (Christinason), the disclosures of which are incorporatedherein by reference. Further details regarding bonded abrasive articlescan be found, for example, in U.S. Pat. Nos. 4,543,107 (Rue), 4,741,743(Narayanan et al.), 4,800,685 (Haynes et al.), 4,898,597 (Hay et al.),4,997,461 (Markhoff-Matheny et al.), 5,037,453 (Narayanan et al.),5,110,332 (Narayanan et al.), and 5,863,308 (Qi et al.) the disclosuresof which are incorporated herein by reference. Further details regardingvitreous bonded abrasives can be found, for example, in U.S. Pat. Nos.4,543,107 (Rue), 4,898,597 (Hay et al.), 4,997,461 (Markhoff-Matheny etal.), 5,094,672 (Giles Jr. et al.), 5,118,326 (Sheldon et al.),5,131,926(Sheldon et al.), 5,203,886 (Sheldon et al.), 5,282,875 (Woodet al.), 5,738,696 (Wu et al.), and 5,863,308 (Qi), the disclosures ofwhich are incorporated herein by reference. Further details regardingnonwoven abrasive articles can be found, for example, in U.S. Pat. No.2,958,593 (Hoover et al.), the disclosure of which is incorporatedherein by reference.

[0160] The present invention provides a method of abrading a surface,the method comprising contacting at least one abrasive particleaccording to the present invention, with a surface of a workpiece; andmoving at least of one the abrasive particle or the contacted surface toabrade at least a portion of said surface with the abrasive particle.Methods for abrading with abrasive particles according to the presentinvention range of snagging (i.e., high pressure high stock removal) topolishing (e.g., polishing medical implants with coated abrasive belts),wherein the latter is typically done with finer grades (e.g., less ANSI220 and finer) of abrasive particles. The abrasive particle may also beused in precision abrading applications, such as grinding cam shaftswith vitrified bonded wheels. The size of the abrasive particles usedfor a particular abrading application will be apparent to those skilledin the art.

[0161] Abrading with abrasive particles according to the presentinvention may be done dry or wet. For wet abrading, the liquid may beintroduced supplied in the form of a light mist to complete flood.Examples of commonly used liquids include: water, water-soluble oil,organic lubricant, and emulsions. The liquid may serve to reduce theheat associated with abrading and/or act as a lubricant. The liquid maycontain minor amounts of additives such as bactericide, antifoamingagents, and the like.

[0162] Abrasive particles according to the present invention may be usedto abrade workpieces such as aluminum metal, carbon steels, mild steels,tool steels, stainless steel, hardened steel, titanium, glass, ceramics,wood, wood like materials, paint, painted surfaces, organic coatedsurfaces and the like. The applied force during abrading typicallyranges from about 1 to about 100 kilograms.

[0163] Advantages and embodiments of this invention are furtherillustrated by the following examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this invention. Allparts and percentages are by weight unless otherwise indicated. Unlessotherwise stated, all examples contained no significant amount of SiO₂,B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅.

EXAMPLES Example 1

[0164] A polyethylene bottle was charged with 132.36 grams (g) ofalumina particles (obtained under the trade designation “APA-0.5” fromCondea Vista, Tucson, Ariz.), 122.64 grams of lanthanum oxide particles(obtained from Molycorp, Inc.), 45 grams of zirconium oxide particles(with a nominal composition of 100 wt-% ZrO₂ (+HfO₂); obtained under thetrade designation “DK-2” from Zirconia Sales, Inc. of Marietta, Ga.) and150.6 grams of distilled water. About 450 grams of alumina milling media(10 mm diameter; 99.9% alumina; obtained from Union Process, Akron,Ohio) were added to the bottle, and the mixture was milled at 120revolutions per minute (rpm) for 4 hours to thoroughly mix theingredients. After the milling, the milling media were removed and theslurry was poured onto a glass (“PYREX”) pan where it was dried using aheat-gun. The dried mixture was ground with a mortar and pestle andscreened through a 70-mesh screen (212-micrometer opening size).

[0165] A small quantity of the dried particles was melted in an arcdischarge furnace (Model No. ST/A 39420; from Centorr Vacuum Industries,Nashua, N.H.). About 1 gram of the dried and sized particles was placedon a chilled copper plate located inside the furnace chamber. Thefurnace chamber was evacuated and then backfilled with Argon gas at 13.8kilopascals (kPa) (2 pounds per square inch (psi)) pressure. An arc wasstruck between an electrode and a plate. The temperatures generated bythe arc discharge were high enough to quickly melt the dried and sizedparticles. After melting was complete, the material was maintained in amolten state for about 10 seconds to homogenize the melt. The resultantmelt was rapidly cooled by shutting off the arc and allowing the melt tocool on its own. Rapid cooling was ensured by the small mass of thesample and the large heat sinking capability of the water chilled copperplate. The fused material was removed from the furnace within one minuteafter the power to the furnace was turned off. Although not wanting tobe bound by theory, it is estimated that the cooling rate of the melt onthe surface of the water chilled copper plate was above 100° C./second.The fused material were transparent glass beads (largest diameter of abead was measured at 2.8 millimeters (mm)).

[0166]FIG. 1 is an X-Ray diffraction pattern of Example 1 glass beads.The broad diffused peak indicates the amorphous nature of the material.

Comparative Example A

[0167] Comparative Example A fused material was prepared as described inExample 1, except the polyethylene bottle was charged with 229.5 gramsof alumina particles (“APA-0.5”), 40.5 grams of lanthanum oxideparticles (obtained from Molycorp, Inc.), 30 grams of zirconium oxideparticles (“DK-2”), 0.6 gram of a dispersing agent (“DURAMAX D-30005”),and 145 grams of distilled water.

[0168]FIG. 2 is a scanning electron microscope (SEM) photomicrograph ofa polished section (prepared as described in Example 6) of fusedComparative Example A material. The photomicrograph shows a crystalline,eutectic-derived microstructure comprising a plurality of colonies. Thecolonies were about 5-20 micrometers in size. Based on powder X-raydiffraction of a portion of Comparative Example A material, andexamination of the polished sample using SEM in the backscattered mode,it is believed that the dark portions in the photomicrograph werecrystalline Al₂O₃, the gray portions crystalline LaAl₁₁O₁₈, and thewhite portions crystalline, monoclinic-ZrO₂.

Example 2

[0169] Example 2 fused material was prepared as described in Example 1,except the polyethylene bottle was charged with 109 grams of aluminaparticles (“APA-0.5”), 101 grams of lanthanum oxide particles (obtainedfrom Molycorp, Inc.), 9 grams of yttrium oxide particles (obtained fromH. C. Starck, Newton, Mass.), 81 grams of zirconium oxide particles(“DK-2”), 0.6 gram of a dispersing agent (“DURAMAX D-30005”), and 145grams of distilled water. The fused material obtained was transparentgreenish glass.

[0170] Several Example 2 glass spheres were placed inside a furnacebetween two flat Al₂O₃ plates. A 300-gram load was applied to the topplate using a dead weight. The glass spheres were heated in air at 930°C. for 1.5 hours. The heat-treated glass spheres were deformed withlarge flat caps on both sides, illustrating that the glass spheresunderwent viscous flow during the heating. Referring to FIG. 3, thearc-melted spheres are on the right, the deformed, heat-treated sphereson the left.

Example 3

[0171] Example 3 fused material was prepared as described in Example 1,except the polyethylene bottle was charged with 20.49 grams of aluminaparticles (“APA-0.5”), 20.45 grams of lanthanum oxide particles(obtained from Molycorp, Inc.), 9.06 grams of yttria-stabilizedzirconium oxide particles (with a nominal composition of 94.6 percent byweight (wt-%) ZrO₂ (+HfO₂) and 5.4 wt-% Y₂O₃; obtained under the tradedesignation “HSY-3” from Zirconia Sales, Inc. of Marietta, Ga.) and 80grams of distilled water. The fused material obtained was transparentglass.

Example 4

[0172] Example 4 fused material was prepared as described in Example 1,except the polyethylene bottle was charged with 21.46 grams of aluminaparticles (“APA-0.5”), 21.03 grams of cerium (IV) oxide (CeO₂)particles, (obtained from Aldrich Chemical Company, Inc., Milwaukee,Wis.), 7.5 grams of zirconium oxide particles (“DK-2”) and 145 grams ofdistilled water. The fused material obtained was dark-brownSEMi-transparent.

Example 5

[0173] Example 5 fused material was prepared as described in Example 1,except the polyethylene bottle was charged with 20.4 grams of aluminaparticles (“APA-0.5”), 22.1 grams of ytterbium oxide particles,(obtained from Aldrich Chemical Company, Inc., Milwaukee, Wis.), 7.5grams of zirconium oxide particles (“DK-2”) and 24.16 grams of distilledwater. The fused material obtained was transparent.

Example 6

[0174] Example 6 material was prepared as described in Example 1, exceptthe polyethylene bottle was replaced by a polyurethane-lined mill whichwas charged with 819.6 grams of alumina particles (“APA-0.5”), 818 gramsof lanthanum oxide particles (obtained from Molycorp, Inc.), 362.4 gramsof yttria-stabilized zirconium oxide particles (with a nominalcomposition of 94.6 wt-% ZrO₂ (+HfO₂) and 5.4 wt-% Y₂O₃; obtained underthe trade designation “HSY-3” from Zirconia Sales, Inc. of Marietta,Ga.), 1050 grams of distilled water and about 2000 grams of zirconiamilling media (obtained from Tosoh Ceramics, Division of Bound Brook,N.J., under the trade designation “YTZ”).

[0175] After grinding and screening, some of the particles were fed intoa hydrogen/oxygen torch flame. The torch used to melt the particles,thereby generating melted glass beads, was a Bethlehem bench bumer PM2Dmodel B, obtained from Bethlehem Apparatus Co., Hellertown, Pa.,delivering hydrogen and oxygen at the following rates. For the innerring, the hydrogen flow rate was 8 standard liters per minute (SLPM) andthe oxygen flow rate was 3 SLPM. For the outer ring, the hydrogen flowrate was 23 (SLPM) and the oxygen flow rate was 9.8 SLPM. The dried andsized particles were fed directly into the torch flame, where they weremelted and transported to an inclined stainless steel surface(approximately 51 centimeters (cm) (20 inches) wide with the slope angleof 45 degrees) with cold water running over (approximately 8liters/minute) the surface to form beads.

[0176] About 50 grams of the beads were placed in a graphite die andhot-pressed using a uniaxial pressing apparatus (obtained under thetrade designation “HP-50”, Thermal Technology Inc., Brea, Calif.). Thehot-pressing was carried out at 960° C. in an argon atmosphere and 13.8megapascals (MPa) (2000 pounds per square inch (2 ksi)) pressure. Theresulting translucent disk was about 48 millimeters in diameter, andabout 5 mm thick. Additional hot-press runs were performed to makeadditional disks. FIG. 4 is an optical photomicrograph of a sectionedbar (2-mm thick) of the hot-pressed material demonstrating itstransparency.

[0177] The density of the resulting hot-pressed glass material wasmeasured using Archimedes method, and found to be within a range ofabout 4.1-4.4 g/cm³. The Youngs' modulus (E) of the resultinghot-pressed glass material was measured using a ultrasonic test system(obtained from Nortek, Richland, Wash. under the trade designation“NDT-140”), and found to be within a range of about 130-150 GPa.

[0178] The average microhardnesses of the resulting hot-pressed materialwas determined as follows. Pieces of the hot-pressed material (about 2-5millimiters in size) were mounted in mounting resin (obtained under thetrade designation “EPOMET” from Buehler Ltd., Lake Bluff, Ill.). Theresulting cylinder of resin was about 2.5 cm (I inch) in diameter andabout 1.9 cm (0.75 inch) tall (i.e., high). The mounted samples werepolished using a conventional grinder/polisher (obtained under the tradedesignation “EPOMET” from Buehler Ltd.) and conventional diamondslurries with the final polishing step using a 1-micrometer diamondslurry (obtained under the trade designation “METADI” from Buehler Ltd.)to obtain polished cross-sections of the sample.

[0179] The microhardness measurements were made using a conventionalmicrohardness tester (obtained under the trade designation “MITUTOYOMVK-VL” from Mitutoyo Corporation, Tokyo, Japan) fitted with a Vickersindenter using a 500-gram indent load. The microhardness measurementswere made according to the guidelines stated in ASTM Test Method E384Test Methods for Microhardness of Materials (1991), the disclosure ofwhich is incorporated herein by reference. The microhardness values werean average of 20 measurements. The average microhardness of thehot-pressed material was about 8.3 GPa.

[0180] The average indentation toughness of the hot-pressed material wascalculated by measuring the crack lengths extending from the apices ofthe vickers indents made using a 500 gram load with a microhardnesstester (obtained under the trade designation “MITUTOYO MVK-VL” fromMitutoyo Corporation, Tokyo, Japan). Indentation toughness (K_(IC)) wascalculated according to the equation:

K _(IC)=0.016 (E/H)^(1/2)(P/c)^(3/2)

[0181] wherein:

[0182] E=Young's Modulus of the material;

[0183] H=Vickers hardness;

[0184] P=Newtons of force on the indenter;

[0185] c=Length of the crack from the center of the indent to its end.

[0186] Samples for the toughness were prepared as described above forthe microhardness test. The reported indentation toughness values are anaverage of 5 measurements. Crack (c) were measured with a digitalcaliper on photomicrographs taken using a scanning electron microscope(“JEOL SEM” (Model JSM 6400)). The average indentation toughness of thehot-pressed material was 1.4 MPa-m™.

[0187] The thermal expansion coefficient of the hot-pressed material wasmeasured using a thermal analyser (obtained from Perkin Elmer, Shelton,Conn., under the trade designation “PERKIN ELMER THERMAL ANALYSER”). Theaverage thermal expansion coefficient was 7.6×10⁻⁶/° C.

[0188] The thermal conductivity of the hot-pressed material was measuredaccording to an ASTM standard “D 5470-95, Test Method A” (1995), thedisclosure of which is incorporated herein by reference. The averagethermal conductivity was 1.15 W/m*K.

[0189] The translucent disk of hot-pressed La₂O₃-Al₂O₃-ZrO₂ glass washeat-treated in a furnace (an electrically heated furnace (obtainedunder the trade designation “Model KKSK-666-3100” from Keith Furnaces ofPico Rivera, Calif.)) as follows. The disk was first heated from roomtemperature (about 25° C.) to about 900° C. at a rate of about 10°C./min and then held at 900° C. for about 1 hour. Next, the disk washeated from about 900° C. to about 1300° C. at a rate of about 10°C./min and then held at 1300° C. for about 1 hour, before cooling backto room temperature by turning off the furnace. Additional runs wereperformed with the same heat-treatment schedule to make additionaldisks.

[0190]FIG. 5 is a scanning electron microscope (SEM) photomicrograph ofa polished section of heat-treated Example 6 material showing the finecrystalline nature of the material. The polished section was preparedusing conventional mounting and polishing techniques. Polishing was doneusing a polisher (obtained from Buehler of Lake Bluff, Ill. under thetrade designation “ECOMET 3 TYPE POLISHER-GRINDER”). The sample waspolished for about 3 minutes with a diamond wheel, followed by threeminutes of polishing with each of 45, 30, 15, 9, and 3-micrometerdiamond slurries. The polished sample was coated with a thin layer ofgold-palladium and viewed using JEOL SEM (Model JSM 840A).

[0191] Based on powder X-ray diffraction of a portion of heat-treatedExample 6 material and examination of the polished sample using SEM inthe backscattered mode, it is believed that the dark portions in thephotomicrograph were crystalline LaAl₁₁O₁₈, the gray portionscrystalline LaAlO₃, and the white portions crystalline cubic/tetragonalZrO₂.

[0192] The density of the heat-treated material was measured usingArchimedes method, and found to be about 5.18 g/cm³. The Youngs' modulus(E) of the heat-treated material was measured using an ultrasonic testsystem (obtained from Nortek, Richland, Wash. under the tradedesignation “NDT-140”), and found to be about 260 GPa. The averagemicrohardness of the heat-treated material was determined as describedabove for the Example 6 glass beads, and was found to be 18.3 GPa. Theaverage fracture toughness (K_(IC)) of the heat-treated material wasdetermined as described above for the Example 6 hot-pressed material,and was found to be 3.3 MPa*m^(1/2).

Examples 7-40

[0193] Examples 7-40 beads were prepared as described in Example 6,except the raw materials and the amounts of raw materials, used arelisted in Table 1, below, and the milling of the raw materials wascarried out in 90 milliliters (ml) of isopropyl alcohol with 200 gramsof the zirconia media (obtained from Tosoh Ceramics, Division of BoundBrook, N.J., under the trade designation “YTZ”) at 120 rpm for 24 hours.The sources of the raw materials used are listed in Table 2, below.TABLE 1 Weight percent of Example components Batch amounts, g 7 La₂O₃:45.06 La₂O₃: 22.53 Al₂O₃: 34.98 Al₂O₃: 17.49 ZrO₂: 19.96 ZrO₂: 9.98 8La₂O₃: 42.29 La₂O₃: 21.15 Al₂O₃: 38.98 Al₂O₃: 19.49 ZrO₂: 8.73 ZrO₂:9.37 9 La₂O₃: 39.51 La₂O₃: 19.76 Al₂O₃: 42.98 Al₂O₃: 21.49 ZrO₂: 17.51ZrO₂: 8.76 10 La₂O₃: 36.74 La₂O₃: 18.37 Al₂O₃: 46.98 Al₂O₃: 23.49 ZrO₂:16.28 ZrO₂: 8.14 11 La₂O₃: 38.65 La₂O₃: 19.33 Al₂O₃: 38.73 Al₂O₃: 19.37ZrO₂: 22.62 ZrO₂: 11.31 12 La₂O₃: 40.15 La₂O₃: 20.08 Al₂O₃: 40.23 Al₂O₃:20.12 ZrO₂: 19.62 ZrO₂: 9.81 13 La₂O₃: 43.15 La₂O₃: 21.58 Al₂O₃: 43.23Al₂O₃: 21.62 ZrO₂: 13.62 ZrO₂: 6.81 14 La₂O₃: 35.35 La₂O₃: 17.68 Al₂O₃:48.98 Al₂O₃: 24.49 ZrO₂: 15.66 ZrO₂: 7.83 15 La₂O₃: 32.58 La₂O₃: 16.2Al₂O₃: 52.98 Al₂O₃: 26.49 ZrO₂: 14.44 ZrO₂: 7.22 16 La₂O₃: 31.20 La₂O₃:15.60 Al₂O₃: 54.98 Al₂O₃: 27.49 ZrO₂: 13.82 ZrO₂: 6.91 17 La₂O₃: 28.43La₂O₃: 14.22 Al₂O₃: 58.98 Al₂O₃: 29.49 ZrO₂: 12.59 ZrO₂: 6.30 18 La₂O₃:26.67 La₂O₃: 13.34 Al₂O₃: 55.33 Al₂O₃: 27.67 ZrO₂: 18.00 ZrO₂: 9.00 19ZrO₂: 5 ZrO₂: 2.5 La₂O₃: 86.5 La₂O₃: 43.25 Al₂O₃: 8.5 Al₂O₃: 4.25 20ZrO₂: 10 ZrO₂: 5.00 La₂O₃: 81.9 La₂O₃: 40.95 Al₂O₃: 8.1 Al₂O₃: 4.05 21CeO₂: 41.4 CeO₂: 20.7 Al₂O₃: 40.6 Al₂O₃: 20.3 ZrO₂: 18 ZrO₂: 9.00 22Al₂O₃: 41.0 Al₂O₃: 20.5 ZrO₂: 17.0 ZrO₂: 8.5 Eu₂O₃: 41.0 Eu₂O₃: 20.5 23Al₂O₃: 41.0 Al₂O₃: 20.5 ZrO₂: 18.0 ZrO₂: 9.0 Gd₂O₃: 41.0 Gd₂O₃: 20.5 24Al₂O₃: 41.0 Al₂O₃: 20.5 ZrO₂: 18.0 ZrO₂: 9.0 Dy₂O₃: 41.0 Dy₂O₃: 20.5 25Al₂O₃: 40.9 Al₂O₃: 20.45 Er₂O₃: 40.9 Er₂O₃: 20.45 ZrO₂: 18.2 ZrO₂: 9.126 La₂O₃: 35.0 La₂O₃: 17.5 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂: 18.12 ZrO₂:9.06 Nd₂O₃: 5.0 Nd₂O₃: 2.50 27 La₂O₃: 35.0 La₂O₃: 17.5 Al₂O₃: 40.98Al₂O₃: 20.49 ZrO₂: 18.12 ZrO₂: 9.06 CeO₂: 5.0 CeO₂: 2.50 28 La₂O₃: 35.0La₂O₃: 17.5 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂: 18.12 ZrO₂: 9.06 Eu₂O₃: 5.0Eu₂O₃: 2.50 29 La₂O₃: 35.0 La₂O₃: 17.5 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂:18.12 ZrO₂: 9.06 Er₂O₃: 5.0 Er₂O₃: 2.50 30 HfO₂: 35.5 HfO₂: 17.75 Al₂O₃:32.5 Al₂O₃: 16.25 La₂O₃: 32.5 La₂O₃: 16.25 31 La₂O₃: 41.7 La₂O₃: 20.85Al₂O₃: 35.4 Al₂O₃: 17.7 ZrO₂: 16.9 ZrO₂: 8.45 MgO: 6.0 MgO: 3.0 32La₂O₃: 39.9 La₂O₃: 19.95 Al₂O₃: 33.9 Al₂O₃: 16.95 ZrO₂: 16.2 ZrO₂: 8.10MgO: 10.0 MgO: 5.0 33 La₂O₃: 43.02 La₂O₃: 21.51 Al₂O₃: 36.5 Al₂O₃: 18.25ZrO₂: 17.46 ZrO₂: 8.73 Li₂CO₃: 3.0 Li₂CO₃: 1.50 34 La₂O₃: 41.7 La₂O₃:20.85 Al₂O₃: 35.4 Al₂O₃: 17.70 ZrO₂: 16.9 ZrO₂: 8.45 Li₂CO₃: 6.0 Li₂CO₃:3.00 35 La₂O₃: 38.8 La₂O₃: 19.4 Al₂O₃: 40.7 Al₂O₃: 20.35 ZrO₂: 17.5ZrO₂: 8.75 Li₂CO₃: 3 Li₂CO₃: 1.50 36 La₂O₃: 43.02 La₂O₃: 21.51 Al₂O₃:36.5 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 TiO₂: 3 TiO₂: 1.50 37 La₂O₃:43.02 La₂O₃: 21.51 Al₂O₃: 36.5 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73NaHCO₃: 3.0 NaHCO₃: 1.50 38 La₂O₃: 42.36 La₂O₃: 21.18 Al₂O₃: 35.94Al₂O₃: 17.97 ZrO₂: 17.19 ZrO₂: 8.60 NaHCO₃: 4.5 NaHCO₃: 2.25 39 La₂O₃:43.02 La₂O₃: 21.51 Al₂O₃: 36.5 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 MgO:1.5 MgO: 0.75 NaHCO₃: 1.5 NaHCO₃: 0.75 TiO₂: 1.5 TiO₂: 0.75 40 La₂O₃:43.0 La₂O₃: 21.50 Al₂O₃: 32.0 Al₂O₃: 16.0 ZrO₂: 12 ZrO₂: 6 SiO₂: 13SiO₂: 65

[0194] TABLE 2 Raw Material Source Alumina particles (Al₂O₃) Obtainedfrom Condea Vista, Tucson, AZ under the trade designation “APA-0.5”Calcium oxide particles (CaO) Obtained from Alfa Aesar, Ward Hill, MACerium oxide particles (CeO₂) Obtained from Rhone-Poulenc, France Erbiumoxide particles (Er₂O₃) Obtained from Aldrich Chemical Co., Milwaukee,WI Europium oxide particles (Eu₂O₃) Obtained from Aldrich Chemical Co.Gadolinium oxide particles (Gd₂O₃) Obtained from Molycorp Inc., MountainPass, CA Hafnium oxide particles (HfO₂) Obtained from Teledyne Wah ChangAlbany Co., Albany, OR Lanthanum oxide particles (La₂O₃) Obtained fromMolycorp Inc. Lithium carbonate particles (Li₂CO₃) Obtained from AldrichChemical Co. Magnesium oxide particles (MgO) Obtained from AldrichChemical Co. Neodymium oxide particles (Nd₂O₃) Obtained from MolycorpInc. Silica particles (SiO₂) Obtained from Alfa Aesar Sodium bicarbonateparticles (NaHCO₃) Obtained from Aldrich Chemical Co. Titanium dioxideparticles (TiO₂) Obtained from Kemira Inc., Savannah, GAYttria-stabilized zirconium oxide particles Obtained from ZirconiaSales, Inc. of (Y-PSZ) Marietta, GA under the trade designation “HSY-3”Dysprosium oxide particles (Dy₂O₃ Obtained from Aldrich Chemical Co.

[0195] Various properties/characteristics of some Example 6-40 materialswere measured as follows. Powder X-ray diffraction (using an X-raydiffractometer (obtained under the trade designation “PHILLIPS XRG 3100”from PHILLIPS, Mahwah, N.J.) with copper K α1 radiation of 1.54050Angstrom)) was used to qualitatively measure phases present in examplematerials. The presence of a broad diffused intensity peak was taken asan indication of the glassy nature of a material. The existence of botha broad peak and well-defined peaks was taken as an indication ofexistence of crystalline matter within a glassy matrix. Phases detectedin various examples are reported in Table 3, below. TABLE 3 Phasesdetected Hot- Exam- via X-ray pressing ple diffraction Color T_(g), ° C.T_(x), ° C. temp, ° C. 6 Amorphous* Clear 834 932 960 7 Amorphous* Clear837 936 960 8 Amorphous* Clear 831 935 — 9 Amorphous* Clear 843 928 — 10Amorphous* Clear 848 920 960 11 Amorphous* Clear 850 923 — 12 Amorphous*Clear 849 930 — 13 Amorphous* Clear 843 932 — 14 Amorphous* Clear 856918 960 15 Amorphous* and Clear/milky 858 914 965 crystalline 16Amorphous* and Clear/milky 859 914 — crystalline 17 Amorphous* andClear/milky 862 912 — crystalline 18 Amorphous* and Clear/milky 875 908— crystalline 19 Crystalline and Milky/clear — amorphous 20 Crystallineand Milky/clear — amorphous 21 Amorphous* and Brown 838 908 960crystalline 22 Amorphous* Intense 874 921 975 yellow/ mustard 23Amorphous* Clear 886 933 985 24 Amorphous* Greenish 881 935 985 25Amorphous* Intense pink 885 934 26 Amorphous* Blue/pink 836 930 965 27Amorphous* Yellow 831 934 965 28 Amorphous* Yellow/gold 838 929 — 29Amorphous* Pink 841 932 — 30 Amorphous* Light green 828 937 960 31Amorphous* Clear 795 901 950 32 Amorphous* Clear 780 870 — 33 Amorphous*Clear 816 942 950 34 Amorphous* Clear 809 934 950 35 Amorphous* Clear/840 922 950 greenish 36 Amorphous* Clear 836 934 950 37 Amorphous* Clear832 943 950 38 Amorphous* Clear 830 943 950 39 Amorphous* Clear/some 818931 950 green 40 Amorphous* Clear 837 1001 —

[0196] r differential thermal analysis (DTA), a material was screened toretain beads in 5 micrometer size range. DTA runs were made (using aninstrument obtained zsch Instruments, Selb, Germany under the tradedesignation “NETZSCH STA TGA”). The amount of each screened sampleplaced in a 100-microliter Al₂O₃ older was 400 milligrams. Each samplewas heated in static air at a rate of ute from room temperature (about25° C.) to 1200° C. eferring to FIG. 6, line 801 is the plotted DTA datafor the Example 6 material. g to FIG. 6 line 801, the material exhibitedan endothermic event at temperature 40° C., as evidenced by the downwardcurve of line 801. It was believed that this s due to the glasstransition (T_(g)) of the material. At about 934° C., an exothermicevent was observed as evidenced by the sharp peak in line 801. It wasbelieved that this event was due to the crystallization (T_(x)) of thematerial. These T_(g) and T_(x) values for other examples are reportedin Table 3, above.

[0197] The hot-pressing temperature at which appreciable glass flowoccurred, as indicated by the displacement control unit of the hotpressing equipment described above, are reported for various examples inTable 3, above.

Example 41

[0198] Example 41 fused material was prepared as described in Example 5,except the polyethylene bottle was charged with 20.49 grams of aluminaparticles (“APA-0.5”), 20.45 grams of lanthanum oxide particles(obtained from Molycorp, Inc.), 9.06 grams of yttria-stabilizedzirconium oxide particles (with a nominal composition of 94.6 wt-% ZrO₂(+HfO₂) and 5.4 wt-% Y₂O₃; obtained under the trade designation “HSY-3”from Zirconia Sales, Inc. of Marietta, Ga.), and 80 grams of distilledwater.

[0199] The resulting amorphous beads were placed in a poyethylene bottle(as in Example 1) together with 200 grams of 2-mm zirconia milling media(obtained from Tosoh Ceramics Bound Brook, N.J. under the tradedesignation “YTZ”). Three hundred grams of distilled water was added tothe bottle, and the mixture milled for 24 hours at 120 rpm to pulverizebeads into powder. The milled material was dried using a heat gun.Fifteen grams of the dried particles were placed in a graphite die andhot-pressed at 960° C. as described in Example 6. The resulting disk wastranslucent.

Example 42

[0200] Example 42 fused amorphous beads were prepared as described inExample 5. About 15 grams of the beads were hot pressed as described inExample 5 except the bottom punch of the graphite die had 2 mm deepgrooves. The resulting material replicated the grooves, indicating verygood flowability of the glass during the heating under the appliedpressure.

Comparative Example B

[0201] Comparative Example B fused material was prepared as described inExample 5, except the polyethylene bottle was charged with 27 grams ofalumina particles (“APA-0.5”), 23 grams of yttria-stabilized zirconiumoxide particles (with a nominal composition of 94.6 wt-% ZrO₂ (+HfO₂)and 5.4 wt-% Y₂O₃; obtained under the trade designation “HSY-3” fromZirconia Sales, Inc. of Marietta, Ga.) and 80 grams of distilled water.The composition of this example corresponds to a eutectic composition inthe Al₂O₃-ZrO₂ binary system. The resulting 100-150 micrometers diameterspheres were partially amorphous, with significant portions ofcrystallinity as evidenced by X-ray diffraction analysis.

Example 43

[0202] A sample (31.25 grams) of amorphous beads prepared as describedin Example 6, and 18.75 grams of beads prepared as described inComparative Example B, were placed in a polyethylene bottle. After 80grams of distilled water and 300 grams of zirconia milling media (TosohCeramics, Bound Brook, N.J. under the trade designation “YTZ”) wereadded to the bottle, the mixture was milled for 24 hours at 120 rpm. Themilled material was dried using a heat gun. Twenty grams of the driedparticles were hot-pressed as described in Example 6. An SEMphotomicrograph of a polished section (prepared as described in Example6) of Example 43 material is shown in FIG. 7. The absence of cracking atinterfaces between the Comparative Example B material (dark areas) andthe Example 6 material (light areas) indicates the establishment of goodbonding.

Examples 44-48

[0203] Examples 44-48 were prepared, including hot-pressing, asdescribed in Example 43, except various additives (see Table 4, below)were used instead of the beads of Comparative Example B. The sources ofthe raw materials used are listed in Table 5, below. TABLE 4 ExampleAdditive Batch, g 44 α-Al₂O₃ LAZ (see Ex.6), 35 α—Al₂O₃, 15 45 PSZ(ZrO₂) LAZ (see Ex.6), 35 PSZ, 15 46 Si₃N₄ LAZ (see Ex.6), 35 Si₃N₄, 547 Diamond (30 LAZ (see Ex.6), 35 micrometers) Diamond, 15 48 Al₂O₃abrasive LAZ (see Ex.6), 35 Microparticles Al₂O₃ abrasiveMicroparticles, 15

[0204] TABLE 5 Raw Material Source Alumina particles (alpha-Al₂O₃)Obtained from Condea Vista, Tucson, AZ under the trade designation“APA-0.5” Yttria-stabilized zirconium oxide particles Obtained fromZirconia Sales, Inc. of (Y-PSZ) Marietta, GA under the trade designation“HSY-3” Silicon nitride particles (Si₃N₄) Obtained from UBE Industries,Japan under the trade designation “E-10” Diamond microparticles (30micrometers) Obtained from the 3M Company, St. Paul Al₂O₃ abrasivemicroparticles (50 micrometers) Obtained from the 3M Company under thedesignation “321 CUBITRON”

[0205] The resulting hot-pressed materials of Examples 44-48 wereobserved to be strong composite materials as determined by visualobservation and handling. FIG. 8 is an SEM micrograph of a polishedcross-section of Example 47 demonstrating good bonding between diamondand the glass.

Examples 49-53

[0206] Examples 49-53 were prepared by heat-treating 15 gram batches ofExample 6 beads in air at temperatures ranging from 1000° C. to 1300° C.for 60 minutes. Heat-treating was performed in an electrically heatedfurnace (obtained under the trade designation “Model KKSK-666-3100” fromKeith Furnaces of Pico Rivera, Calif.). The resulting heat-treatedmaterials were analyzed using powder X-ray diffraction as describedabove for Examples 6-40. The results are summarized in Table 6, below.

[0207] The average microhardnesses of Examples 49-53 beads (about 125micrometers in size) were measured as described in Example 6. TABLE 6Heat-treatment Phases temperature, detected via Hardness, Example ° C.X-ray diffraction Color GPa 49 900 Amorphous Clear  7.5 ± 0.3 50 1000LaAlO₃; Clear/milky  8.4 ± 0.2 La₂Zr₂O₇ 51 1100 LaAlO₃; Clear/milky 10.3± 0.2 La₂Zr₂O₇; Cubic/tetragonal ZrO₂ 52 1200 LaAlO₃; Clear/milky 11.8 ±0.2 Cubic/tetragonal ZrO₂; LaAl₁₁O₁₈ 53 1300 LaAlO₃; Opaque 15.7 ± 0.4Cubic/tetragonal ZrO₂; LaAl₁₁O₁₈

Grinding Performance of Examples 6 and 6A and Comparative Examples C-E

[0208] Example 6 hot-pressed material was crushed by using a “Chipmunk”jaw crusher (Type VD, manufactured by BICO Inc., Burbank, Calif.) into(abrasive) particles and graded to retain the −25+30 mesh fraction(i.e., the fraction collected between 25-micrometer opening and30-micrometer opening size sieves) and −30+35 mesh fractions (i.e., thefraction collected between 30-micrometer opening size and 35-micrometeropening size sieves) (USA Standard Testing Sieves). These two meshfractions were combined to provide a 50/50 blend. The blended materialwas heat treated as described in Example 6. Thirty grams of theresulting glass-ceramic abrasive particles were incorporated into acoated abrasive disc. The coated abrasive disc was made according toconventional procedures. The glass-ceramic abrasive particles werebonded to 17.8 cm diameter, 0.8 mm thick vulcanized fiber backings(having a 2.2 cm diameter center hole) using a conventional calciumcarbonate-filled phenolic make resin (48% resole phenolic resin, 52%calcium carbonate, diluted to 81% solids with water and glycol ether)and a conventional cryolite-filled phenolic size resin (32% resolephenolic resin, 2% iron oxide, 66% cryolite, diluted to 78% solids withwater and glycol ether). The wet make resin weight was about 185 g/m².Immediately after the make coat was applied, the glass-ceramic abrasiveparticles were electrostatically coated. The make resin was precured for120 minutes at 88° C. Then the cryolite-filled phenolic size coat wascoated over the make coat and abrasive particles. The wet size weightwas about 850 g/m². The size resin was cured for 12 hours at 99° C. Thecoated abrasive disc was flexed prior to testing.

[0209] Example 6A coated abrasive disk was prepared as described forExample 6 except the Example 6A abrasive particles were obtained bycrushing a hot-pressed and heat-treated Example 6 material, rather thancrushing then heat-treating.

[0210] Comparative Example C coated abrasive discs were prepared asdescribed for Example 6 (above), except heat-treated fused aluminaabrasive particles (obtained under the trade designation “ALODUR BFRPL”from Triebacher, Villach, Austria) was used in place of the Example 6glass-ceramic abrasive particles.

[0211] Comparative Example D coated abrasive discs were prepared asdescribed for Example 6 (above), except alumina-zirconia abrasiveparticles (having a eutectic composition of 53% Al₂O₃ and 47% ZrO₂;obtained under the trade designation “NORZON” from Norton Company,Worcester, Mass.) were used in place of the Example 6 glass-ceramicabrasive particles.

[0212] Comparative Example E coated abrasive discs were prepared asdescribed above except sol-gel-derived abrasive particles (marketedunder the trade designation “321 CUBITRON” from the 3M Company, St.Paul, Minn.) was used in place of the Example 6 glass-ceramic abrasiveparticles.

[0213] The grinding performance of Example 6 and Comparative ExamplesC-E coated abrasive discs were evaluated as follows. Each coatedabrasive disc was mounted on a beveled aluminum back-up pad, and used togrind the face of a pre-weighed 1.25 cm×18 cm×10 cm 1018 mild steelworkpiece. The disc was driven at 5,000 rpm while the portion of thedisc overlaying the beveled edge of the back-up pad contacted theworkpiece at a load of 8.6 kilograms. Each disc was used to grind anindividual workpiece in sequence for one-minute intervals. The total cutwas the sum of the amount of material removed from the workpiecesthroughout the test period. The total cut by each sample after 12minutes of grinding as well as the cut at the 12th minute (i.e., thefinal cut) are reported in Table 6, below. The Example 6 results are anaverage of two discs, where as one disk was tested for each of Example6A, and Comparative Examples C, D, and E. TABLE 6 Example Total cut, gFinal cut, g 6 1163 92 6A 1197 92 Comp. C 514 28 Comp. D 689 53 Comp. E1067 89

[0214] Various modifications and alterations of this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. Glass comprising Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, wherein at least 85 percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,based on the total weight of the glass.
 2. The glass according to claim1 collectively comprising at least 80 percent by weight of the Al₂O₃,REO, and ZrO₂, based on the total weight of the glass.
 3. Ceramiccomprising the glass according to claim
 1. 4. A method for making glasscomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 85 percent by weight of the glass collectively comprises theAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on the total weightof the glass, the method comprising: melting sources of at least Al₂O₃,REO, and at least one of ZrO₂ or HfO₂ to provide a melt; and cooling themelt to provide the glass.
 5. A method for making ceramic comprisingglass, wherein the glass comprises Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein at least 85 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass, the method comprising: melting sources of atleast Al₂O₃, REO, and at least one of ZrO₂ or HfO₂ to provide a melt;and cooling the melt to provide the ceramic.
 6. A method for making anarticle comprising glass comprising Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein at least 85 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass, the method comprising: melting at leastsources of Al₂O₃, REO, and at least one of ZrO₂ or HfO₂ to provide amelt; cooling the melt to provide glass beads comprising glasscomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 85 percent by weight of the glass collectively comprises theAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on the total weightof the glass, the glass having a T_(g); heating the glass beads abovethe T_(g) such that the glass beads coalesce to form a shape; andcooling the coalesced shape to provide the article.
 7. A method formaking an article comprising glass comprising Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, wherein at least 70 percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,and less than 15 percent by weight SiO₂ and less than 15 percent byweight B₂O₃, based on the total weight of the glass, the methodcomprising: melting at least sources of Al₂O₃, REO, and at least one ofZrO₂ or HfO₂ to provide a melt; cooling the melt to provide glass beadscomprising glass comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein at least 70 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 15 percent by weight SiO₂, and less than 15 percent by weight B₂O₃,based on the total weight of the glass, the glass having a T_(g);heating the glass beads above the T_(g) such that the glass beadscoalesce to form a shape; and cooling the coalesced shape to provide thearticle.
 8. A method for making an article comprising glass comprisingAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 70percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 30 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass, the method comprising: melting at least sources of Al₂O₃, REO,and at least one of ZrO₂ or HfO₂ to provide a melt; cooling the melt toprovide glass beads comprising glass comprising Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, wherein at least 70 percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,and less than 30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅,based on the total weight of the glass, the glass having a T_(g);heating the glass beads above the T_(g) such that the glass beadscoalesce to form a shape; and cooling the coalesced shape to provide thearticle.
 9. A method for making an article comprising glass comprisingAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 85percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, based on the total weight of theglass, the method comprising: melting at least sources of Al₂O₃, REO,and at least one of ZrO₂ or HfO₂ to provide a melt; cooling the melt toprovide glass beads comprising glass comprising Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, wherein at least 85 percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,based on the total weight of the glass, the glass having a T_(g);converting the glass beads to provide glass powder; heating the glasspowder above the T_(g) such that the glass powder coalesces to form ashape; and cooling the coalesced shape to provide the article.
 10. Amethod for making an article comprising glass comprising Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, wherein at least 70 percent by weight ofthe glass collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, and less than 15 percent by weight SiO₂, and less than 15percent by weight B₂O₃, based on the total weight of the glass, themethod comprising: melting at least sources of Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂ to provide a melt; cooling the melt to provide glassbeads comprising glass comprising Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein at least 70 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 15 percent by weight SiO₂, and less than 15 percent by weight B₂O₃,based on the total weight of the glass, the glass having a T_(g);converting the glass beads to provide glass powder; heating the glasspowder above the T_(g) such that the glass powder coalesces to form ashape; and cooling the coalesced shape to provide the article.
 11. Amethod for making an article comprising glass comprising Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, wherein at least 70 percent by weight ofthe glass collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, and less than 30 percent by weight collectively SiO₂,B₂O₃, and P₂O₅, based on the total weight of the glass, the methodcomprising: melting at least sources of Al₂O₃, REO, and at least one ofZrO₂ or HfO₂ to provide a melt; cooling the melt to provide glass beadscomprising glass comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein at least 70 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass, the glass having a T_(g); converting theglass beads to provide glass powder; heating the glass powder above theT_(g) such that the glass powder coalesces to form a shape; and coolingthe coalesced shape to provide the article.
 12. Ceramic comprising atleast 75 percent by volume glass, the glass comprising Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, wherein at least 85 percent by weight ofthe glass collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass.
 13. The ceramicaccording to claim 12 wherein the glass collectively comprising at least85 percent by weight of the Al₂O₃, REO, and ZrO₂, based on the totalweight of the glass.
 14. Glass-ceramic comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, wherein at least 85 percent by weight of theglass-ceramic collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass-ceramic.
 15. Theglass-ceramic according to claim 14 collectively comprising at least 85percent by weight of the Al₂O₃, REO, and ZrO₂, based on the total weightof the glass-ceramic.
 16. Glass-ceramic comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, wherein at least 70 percent by weight of theglass-ceramic collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, and less than 15 percent by weight SiO₂ and less than 15percent by weight B₂O₃, based on the total weight of the glass-ceramic.17. The glass-ceramic according to claim 16 collectively comprising atleast 70 percent by weight of the Al₂O₃, REO, and ZrO₂, based on thetotal weight of the glass-ceramic.
 18. Glass-ceramic comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein at least 70 percent byweight of the glass-ceramic collectively comprises the Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, and less than 30 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass-ceramic.
 19. The glass-ceramic according to claim 18 collectivelycomprising at least 70 percent by weight of the Al₂O₃, REO, and ZrO₂,based on the total weight of the glass-ceramic.
 20. Glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein theceramic (a) exhibits a microstructure comprising crystallites having anaverage crystallite size of less than 1 micrometer, and (b) is free ofeutectic microstructure features. 21 The glass-ceramic according toclaim 20 comprising the Al₂O₃, REO, and ZrO₂.
 22. A method for makingglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 85 percent by weight of the glass-ceramic collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass-ceramic, the method comprising: heat-treatingglass comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, whereinat least 85 percent by weight of the glass collectively comprises theAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on the total weightof the glass to provide the glass-ceramic.
 23. A method for makingglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 85 percent by weight of the glass-ceramic collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass-ceramic, the method comprising: heat-treatingceramic comprising glass, wherein the glass comprises Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, wherein at least 85 percent by weight of theglass collectively comprises the Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, based on the total weight of the glass to provide theglass-ceramic.
 24. A method for making glass-ceramic comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein at least 70 percent byweight of the glass-ceramic collectively comprises the Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, and less than 15 percent by weight SiO₂and less than 15 percent by weight B₂O₃, based on the total weight ofthe glass-ceramic, the method comprising: heat-treating glass comprisingAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 70percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 15 percent by weightSiO₂ and less than 15 percent by weight B₂O₃, based on the total weightof the glass to provide the glass-ceramic.
 25. A method for makingglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 70 percent by weight of the glass-ceramic collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 15 percent by weight SiO₂, and less than 15 percent by weight B₂O₃,based on the total weight of the glass-ceramic, the method comprising:heat-treating ceramic comprising glass, wherein the glass comprisesAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 70percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 15 percent by weightSiO₂, and less than 15 percent by weight B₂O₃, based on the total weightof the glass to provide the glass-ceramic.
 26. A method for makingglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein at least 70 percent by weight of the glass-ceramic collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass-ceramic, the method comprising:heat-treating glass comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein at least 70 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass to provide the glass-ceramic.
 27. A methodfor making glass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein at least 70 percent by weight of the glass-ceramiccollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,and less than 30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅,based on the total weight of the glass-ceramic, the method comprising:heat-treating ceramic comprising glass, wherein the glass comprisesAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 70percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 30 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass to provide the glass-ceramic.
 28. A method for makingglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,the method comprising: heat-treating glass comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂ to provide the glass-ceramic, wherein theglass-ceramic (a) exhibits a microstructure comprising crystalliteshaving an average crystallite size of less than 1 micrometer, and (b) isfree of eutectic microstructure features.
 29. A method for makingglass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,the method comprising: heat-treating ceramic comprising glass, whereinthe glass comprises Al₂O₃, REO, and at least one of ZrO₂ or HfO₂ toprovide the glass-ceramic wherein the glass-ceramic (a) exhibits amicrostructure comprising crystallites having an average crystallitesize of less than 1 micrometer, and (b) is free of eutecticmicrostructure features.
 30. A method for making a glass-ceramicarticle, the method comprising: converting glass to provide glasspowder, the glass comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein at least 85 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass, the glass having a T_(g); heating the glasspowder above the T_(g) such that the glass powder coalesces to form ashape; cooling the coalesced shape to provide a glass article; andheat-treating the glass article to provide a glass-ceramic article. 31.A method for making a glass-ceramic article, the method comprising:converting glass to provide glass powder, the glass comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein at least 70 percent byweight of the glass collectively comprises the Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, and less than 15 percent by weight SiO₂, and lessthan 15 percent by weight B₂O₃, based on the total weight of the glass,the glass having a T_(g); heating the glass powder above the T_(g) suchthat the glass powder coalesces to form a shape; cooling the coalescedshape to provide a glass article; and heat-treating the glass article toprovide a glass-ceramic article.
 32. A method for making a glass-ceramicarticle, the method comprising: converting glass to provide glasspowder, the glass comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein at least 70 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO, and less than30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on thetotal weight of the glass, the glass having a T_(g); heating the glasspowder above the T_(g) such that the glass powder coalesces to form ashape; cooling the coalesced shape to provide a glass article; andheat-treating the glass article to provide a glass-ceramic article. 33.Glass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,wherein the glass-ceramic (a) exhibits a microstructure comprisingcrystallites having an average crystallite size of less than 200nanometers and (b) has a density of at least 90% of theoretical density.34. Glass-ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein the glass-ceramic (a) exhibits a microstructure comprisingcrystallites, wherein none of the crystallites are greater than 200nanometers in size and (b) has a density of at least 90% of theoreticaldensity.
 35. Glass-ceramic comprising Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, wherein the glass-ceramic (a) exhibits a microstructurecomprising crystallites, wherein at least a portion of the crystallitesare not greater than 150 nanometers in size and (b) has a density of atleast 90% of theoretical density.
 36. Ceramic comprising at least 75percent by volume crystalline ceramic, the crystalline ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein theceramic (a) exhibits a microstructure comprising crystallites having anaverage crystallite size of less than 200 nanometers and (b) has adensity of at least 90% of theoretical density.
 37. Ceramic comprisingat least 75 percent by volume crystalline ceramic, the crystallineceramic comprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, whereinthe ceramic (a) exhibits a microstructure comprising crystallites,wherein none of the crystallites are greater than 200 nanometers in sizeand (b) has a density of at least 90% of theoretical density. 38.Ceramic comprising at least 75 percent by volume crystalline ceramic,the crystalline ceramic comprising Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein the ceramic (a) exhibits a microstructure comprisingcrystallites, wherein at least a portion of the crystallites are notgreater than 150 nanometers in size and (b) has a density of at least90% of theoretical density.
 39. Ceramic comprising at least 75 percentby volume crystalline ceramic, the crystalline ceramic comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites having an average crystallitesize not greater than 200 nanometer, in size and (b) has a density of atleast 90% of theoretical density.
 40. The ceramic according to claim 39wherein the crystalline ceramic collectively comprising Al₂O₃, REO, andZrO₂, based on the total weight of the crystalline ceramic.
 41. Abrasiveparticle comprising a glass-ceramic comprising Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, wherein at least 85 percent by weight of theglass-ceramic collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass-ceramic. 42.Abrasive particle comprising a glass-ceramic comprising Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, wherein at least 70 percent by weight ofthe glass-ceramic collectively comprises the Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, and less than 15 percent by weight SiO₂ and lessthan 15 percent by weight B₂O₃, based on the total weight of theglass-ceramic.
 43. Abrasive particle comprising a glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 70 percent by weight of the glass-ceramic collectively comprisesthe Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and less than 30percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the totalweight of the glass-ceramic.
 44. A method for making abrasive particles,the method comprising: heat-treating glass particles comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein at least 85 percent byweight of the glass collectively comprises the Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, based on the total weight of the glass particles,to provide glass-ceramic abrasive particles.
 45. A method for makingabrasive particles, the method comprising: heat-treating particlescomprising glass, wherein the glass comprises Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, wherein at least 85 percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,based on the total weight of the glass particles, to provideglass-ceramic abrasive particles.
 46. A method for making abrasiveparticles, the method comprising: heat-treating glass comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein at least 85 percent byweight of the glass collectively comprises the Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, based on the total weight of the glass, to provideglass-ceramic; and converting the glass-ceramic to provide abrasiveparticles.
 47. A method for making abrasive particles, the methodcomprising: heat-treating ceramic comprising glass, wherein the glasscomprises Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least85 percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, based on the total weight of theglass, to provide glass-ceramic; and converting the glass-ceramic toprovide abrasive particles.
 48. A method for making abrasive particles,the method comprising: heat-treating glass particles comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein at least 70 percent byweight of the glass collectively comprises the Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, and less than 15 percent by weight SiO₂ and lessthan 15 percent by weight B₂O₃, based on the total weight of the glassparticles, to provide glass-ceramic abrasive particles.
 49. A method formaking abrasive particles, the method comprising: heat-treatingparticles comprising glass, wherein the glass comprises Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, wherein at least 70 percent by weight ofthe glass collectively comprises the Al₂O₃, REO, and at least one ofZrO₂ or HfO₂, and less than 15 percent by weight SiO₂, and less than 15percent by weight B₂O₃, based on the total weight of the glassparticles, to provide glass-ceramic abrasive particles.
 50. A method formaking abrasive particles, the method comprising: heat-treating glasscomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein atleast 70 percent by weight of the glass collectively comprises theAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, and less than 15 percentby weight SiO₂ and less than 15 percent by weight B₂O₃, based on thetotal weight of the glass, to provide glass-ceramic; and converting theglass-ceramic to provide abrasive particles.
 51. A method for makingabrasive particles, the method comprising: heat-treating ceramiccomprising glass, wherein the glass comprises Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂, wherein at least 70 percent by weight of the glasscollectively comprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂,and less than 15 percent by weight SiO₂ and less than 15 percent byweight B₂O₃, based on the total weight of the glass, to provideglass-ceramic; and converting the glass-ceramic to provide abrasiveparticles.
 52. A method for making abrasive particles, the methodcomprising: heat-treating glass particles comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, wherein at least 70 percent by weight of theglass collectively comprises the Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, and less than 30 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass particles, to provideglass-ceramic abrasive particles.
 53. A method for making abrasiveparticles, the method comprising: heat-treating particles comprisingglass, wherein the glass comprises Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein at least 70 percent by weight of the glass collectivelycomprises the Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, and lessthan 30 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass particles, to provide glass-ceramicabrasive particles.
 54. A method for making abrasive particles, themethod comprising: heat-treating glass comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, wherein at least 70 percent by weight of theglass collectively comprises the Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, and less than 30 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass, to provide glass-ceramic;and converting the glass-ceramic to provide abrasive particles.
 55. Amethod for making abrasive particles, the method comprising:heat-treating ceramic comprising glass, wherein the glass comprisesAl₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein at least 70percent by weight of the glass collectively comprises the Al₂O₃, REO,and at least one of ZrO₂ or HfO₂, and less than 30 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass, to provide glass-ceramic; and converting the glass-ceramic toprovide abrasive particles.
 56. A method for making abrasive particles,the method comprising: heat-treating glass particles comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂ to provide glass-ceramic abrasiveparticles, wherein the glass-ceramic (a) exhibits a microstructurecomprising crystallites having an average crystallite size of less than1 micrometer, and (b) is free of eutectic microstructure features.
 57. Amethod for making abrasive particles, the method comprising:heat-treating particles comprising glass, wherein the glass comprisesAl₂O₃, REO, and at least one of ZrO₂ or HfO₂ to provide glass-ceramicabrasive particles, wherein the glass-ceramic (a) exhibits amicrostructure comprising crystallites having an average crystallitesize of less than 1 micrometer, and (b) is free of eutecticmicrostructure features.
 58. A method for making abrasive particles, themethod comprising: heat-treating glass comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂ to provide glass-ceramic, wherein theglass-ceramic (a) exhibits a microstructure comprising crystalliteshaving an average crystallite size of less than 1 micrometer, and (b) isfree of eutectic microstructure features; and converting theglass-ceramic to provide abrasive particles.
 59. A method for makingabrasive particles, the method comprising: heat-treating ceramiccomprising glass, wherein the glass comprises Al₂O₃, REO, and at leastone of ZrO₂ or HfO₂ to provide glass-ceramic, wherein the glass-ceramic(a) exhibits a microstructure comprising crystallites having an averagecrystallite size of less than 1 micrometer, and (b) is free of eutecticmicrostructure features; and converting the glass-ceramic to provideabrasive particles.
 60. Abrasive particle comprising a glass-ceramiccomprising Al₂O₃, REO, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystalliteshaving an average crystallite size of less than 200 nanometers and (b) adensity of at least 90% of theoretical density.
 61. The abrasiveparticle according to claim 60 comprising at least 90 percent by volumeof said ceramic, based on the total volume of said abrasive particle.62. Abrasive particle comprising a glass-ceramic comprising Al₂O₃, REO,and at least one of ZrO₂ or HfO₂ wherein the glass-ceramic (a) exhibitsa microstructure comprising crystallites, wherein none of thecrystallites are greater than 200 nanometers in size and (b) a densityof at least 90% of theoretical density.
 63. The abrasive particleaccording to claim 62 comprising at least 90 percent by volume of saidceramic, based on the total volume of said abrasive particle. 64.Abrasive particle comprising a glass-ceramic comprising Al₂O₃, REO, andat least one of ZrO₂ or HfO₂, wherein the glass-ceramic (a) exhibits amicrostructure comprising crystallites, wherein at least a portion ofthe crystallites are not greater than 150 nanometers in size and (b) adensity of at least 90% of theoretical density.
 65. The abrasiveparticle according to claim 64 comprising at least 90 percent by volumeof said ceramic, based on the total volume of said abrasive particle.66. Abrasive particle comprising ceramic comprising at least 75 percentby volume crystalline ceramic, the crystalline ceramic comprising Al₂O₃,REO, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites having an average crystallitesize of less than 200 nanometers and (b) a density of at least 90% oftheoretical density.
 67. The abrasive particle according to claim 66comprising at least 90 percent by volume of said ceramic, based on thetotal volume of said abrasive particle.
 68. Abrasive particle comprisingceramic comprising at least 75 percent by volume crystalline ceramic,the crystalline ceramic comprising Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein the ceramic (a) exhibits a microstructure comprisingcrystallites, wherein none of the crystallites are greater than 200nanometers in size and (b) a density of at least 90% of theoreticaldensity.
 69. The abrasive particle according to claim 68 comprising atleast 90 percent by volume of said ceramic, based on the total volume ofsaid abrasive particle.
 70. Abrasive particle comprising ceramiccomprising at least 75 percent by volume crystalline ceramic, thecrystalline ceramic comprising Al₂O₃, REO, and at least one of ZrO₂ orHfO₂, wherein the ceramic (a) exhibits a microstructure comprisingcrystallites, wherein at least a portion of the crystallites are notgreater than 150 nanometers in size and (b) a density of at least 90% oftheoretical density.
 71. The abrasive particle according to claim 70comprising at least 90 percent by volume of said ceramic, based on thetotal volume of said abrasive particle.
 72. Abrasive particle comprisingceramic comprising at least 75 percent by volume crystalline ceramic,the crystalline ceramic comprising Al₂O₃, REO, and at least one of ZrO₂or HfO₂, wherein the ceramic (a) exhibits a microstructure comprisingcrystallites having an average crystallite size not greater than 200nanometer, in size and (b) a density of at least 90% of theoreticaldensity.
 73. The abrasive particle according to claim 72 comprising atleast 90 percent by volume of said ceramic, based on the total volume ofsaid abrasive particle.
 74. A plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles comprise alpha Al₂O₃, crystalline ZrO₂, and a firstcomplex Al₂O₃.REO, wherein at least one of the alpha Al₂O₃, thecrystalline ZrO₂, or the first complex Al₂O₃-REO has an average crystalsize not greater than 150 nanometers, and wherein the abrasive particlesof the portion have a density of at least 90 percent of theoreticaldensity.
 75. An abrasive article comprising a binder and a plurality ofabrasive particles, wherein at least a portion of the abrasive particlescomprise alpha Al₂O₃, crystalline ZrO₂, and a first complex Al₂O₃.REO,wherein at least one of the alpha Al₂O₃, the crystalline ZrO₂, or thefirst complex Al₂O₃.REO has an average crystal size not greater than 150nanometers, and wherein the abrasive particles of the portion have adensity of at least 90 percent of theoretical density.
 76. A method ofabrading a surface, the method comprising: providing an abrasive articlecomprising a binder and a plurality of abrasive particles, wherein atleast a portion of the abrasive particles comprise alpha Al₂O₃,crystalline ZrO₂, and a first complex Al₂O₃.REO, wherein at least one ofthe alpha Al₂O₃, the crystalline ZrO₂, or the first complex Al₂O₃.REOhas an average crystal size not greater than 150 nanometers, and whereinthe abrasive particles of the portion have a density of at least 90percent of theoretical density; contacting at least one of the abrasiveparticles comprising the alpha Al₂O₃, the crystalline ZrO₂, and thefirst complex Al₂O₃.REO with a surface of a workpiece; and moving atleast one of the contacted abrasive particles comprising the alphaAl₂O₃, the crystalline ZrO₂, and the first complex Al₂O₃.REO or thecontacted surface to abrade at least a portion of the surface with thecontacted abrasive particle comprising the alpha Al₂O₃, the crystallineZrO₂, and the first complex Al₂O₃.REO.
 77. A plurality of abrasiveparticles having a specified nominal grade, wherein at least a portionof the plurality of abrasive particles comprise a first complexAl₂O₃.REO, a second, different complex Al₂O₃.REO, and crystalline ZrO₂,wherein for at least one of the first complex Al₂O₃.REO, the secondcomplex Al₂O₃.REO, or the crystalline ZrO₂, wherein at least 90 percentby number of crystal sizes thereof are not greater than 200 nanometers,and wherein the abrasive particles of the portion have a density of atleast 90 percent of theoretical density.
 78. An abrasive articlecomprising a binder and a plurality of abrasive particles, wherein atleast a portion of the abrasive particles comprise a first complexAl₂O₃.REO, a second, different complex Al₂O₃.REO, and crystalline ZrO₂,wherein in such portion, for at least one of the first complexAl₂O₃.REO, the second complex Al₂O₃.REO, or the crystalline ZrO₂,wherein at least 90 percent by number of crystal sizes thereof are notgreater than 200 nanometers, and wherein the abrasive particles of theportion have a density of at least 90 percent of theoretical density.79. A method of abrading a surface, the method comprising: providing anabrasive article comprising a binder and a plurality of abrasiveparticles, wherein at least a portion of the abrasive particles comprisea first complex Al₂O₃.REO, a second, different complex Al₂O₃.REO, andcrystalline ZrO₂, wherein in such portion, for at least one of the firstcomplex Al₂O₃.REO, the second complex Al₂O₃.REO, or the crystallineZrO₂, wherein at least 90 percent by number of crystal sizes thereof arenot greater than 200 nanometers, and wherein the abrasive particles ofthe portion have a density of at least 90 percent of theoreticaldensity; contacting at least one of the abrasive particles comprisingthe first complex Al₂O₃.REO, the second complex Al₂O₃.REO, and thecrystalline ZrO₂ with a surface of a workpiece; and moving at least oneof the contacted abrasive particles comprising the first complexAl₂O₃.REO, the second complex Al₂O₃.REO, and the crystalline ZrO₂ or thecontacted surface to abrade at least a portion of the surface with thecontacted abrasive particle comprising the first complex Al₂O₃.REO, thesecond complex Al₂O₃.REO, and the crystalline ZrO₂.